Potential December 12th-13th threat

[NEGa]

I am not a met but in my opinion from examining maps/forecasts to the best of my ability, I feel the higher elevations of northeast ga could potentially see an inch of snowfall on sunday. yes it is not eched in stone but I think there will be enough precip and instability on the backend to produce a couple hours of snow.

i guess what caught my attention was the dawsonville to gainesville north part. that is a wide area - granted brasstown bald, for example, could get some snow. i took from your post that most people above that line would get an inch of snow.

Sunday...Cloudy with a 40 percent chance of snow or rain. Windy. Highs in the upper 30s.

Sunday Night...Mostly cloudy with a 40 percent chance of snow showers. Windy. Lows around 16.

Monday...Sunny...windy. Highs around 30.

I would not drive an hour for this.

i wouldnt either. basically similar to my forecast. accumulations little to none for most. unfortunately. i was hoping this one would start trending in our favor with all the cold air, but doesnt appear to be happening unless we get a miracle

[Cheeznado]

18Z NAM trending slower and deeper......

[neatlburbwthrguy]

i guess what caught my attention was the dawsonville to gainesville north part. that is a wide area - granted brasstown bald, for example, could get some snow. i took from your post that most people above that line would get an inch of snow.

i wouldnt either. basically similar to my forecast. accumulations little to none for most. unfortunately. i was hoping this one would start trending in our favor with all the cold air, but doesnt appear to be happening unless we get a miracle

im sorry i mis-worded my comment. however, i dont think you getting a dusting to half inch of snow is out of the question at this point...

[UNCCmetgrad]

Yeah, you're right. This run extends the cold wave to Thursday...and is it just me or has 12z model runs been significantly colder than 0z thus far?

You want to talk a total and complete mess, that's what the GFS is showing. It doesn't take a whole lot of anything (sn, ip or zr) to cause a mess with how cold it's been. This could definitely be one of those situations where you see zr sticking to pavement which almost never happens here.

Looking at bufkit profiles for Wednesday evening shows precip starting as ice pellets then transitioning to frz rain with about 0.1 in of QPF. With temperatures around 30 and cold ground temps that amount would be just enough to turn roads into skating rinks. With the way people drive around Charlotte that would be entertaining to watch. This has shown up now for the past several runs so something to stay mindful about.

BTW... just got back from Green Bay, watching the Packers play at Lambeau Field. Quite a site to see. Temperatures were around 25 during the game but the wind chill hovered just above 10 degrees. You haven't really tailgated until you look down and top of your beer has begun to ice over.

[rosie]

i guess what caught my attention was the dawsonville to gainesville north part. that is a wide area - granted brasstown bald, for example, could get some snow. i took from your post that most people above that line would get an inch of snow.

i wouldnt either. basically similar to my forecast. accumulations little to none for most. unfortunately. i was hoping this one would start trending in our favor with all the cold air, but doesnt appear to be happening unless we get a miracle

One can hope, guess we will be floodlighting it again!

[neatlburbwthrguy]

18Z NAM trending slower and deeper......

to the untrained/amateur folks like myself, i take it this is possibly a good sign....?

[chapelhillwx]

The NAM is looking at least a little interesting for me here in central NC. It looks like it's an all-out race between cold air and precip.... at hour 84 my 850 temp is below zero with .10-.25 precip falling. We'll see, I guess.

[Cheeznado]

Looking at bufkit profiles for Wednesday evening shows precip starting as ice pellets then transitioning to frz rain with about 0.1 in of QPF. With temperatures around 30 and cold ground temps that amount would be just enough to turn roads into skating rinks. With the way people drive around Charlotte that would be entertaining to watch. This has shown up now for the past several runs so something to stay mindful about.

BTW... just got back from Green Bay, watching the Packers play at Lambeau Field. Quite a site to see. Temperatures were around 25 during the game but the wind chill hovered just above 10 degrees. You haven't really tailgated until you look down and top of your beer has begun to ice over.

This thread is about the 12th-13th- discussion about the potential ice event next week should get its own thread or be moved to the general December thread.

Thanks

[burgertime]

The NAM is looking at least a little interesting for me here in central NC. It looks like it's an all-out race between cold air and precip.... at hour 84 my 850 temp is below zero with .10-.25 precip falling. We'll see, I guess.

Yea the problem is surface temps. Like you said it's that race going on which usually leaves us spun out and watching the winners from a few feet away.

[WXinCanton]

This thread is about the 12th-13th- discussion about the potential ice event next week should get its own thread or be moved to the general December thread.

Thanks

you seem more optimistic than I remember?? You looking to go up to the mountains?

[EmersonGA]

I am in Dunwoody. But if me driving an hour or so north towards dawsonville or north of gainesville means I will see a good bit more snow than I will definitely do so, especially since it will be on a Sunday and I won't have to be at work. You gotta think north ga from dawsonville gainesville north should pick up an inch out of this...

Take 136 from Jasper over towards Dawsonville. You go up Burnt Mountain/Mt. Oglethorpe and they do pretty well in these situations. They usually get an inch when I see flurries at the house. The driving can be pretty dangerous though. I've had a couple of scary experiences up there.

[SnoJoe]

From GSP

.LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/...

-- Changed Discussion --AS OF 245 PM THURSDAY...THE MEDIUM RANGE PICKS UP AT 00Z MONDAY...BY

WHICH TIME OUR TRANSITION TO A NW FLOW SNOW EVENT SHOULD BECOMPLETE. IN GENERAL...THE 00Z RUN OF THE ECMWF WAS FAVORED FOR

GUIDANCE THROUGH THE MIDDLE OF NEXT WEEK. AS A DEEP UPPER LOW SPINS

AWAY TO OUR N AND NE DURING THE EARLY PART OF THE WEEK...A DEEP COLD

NW FLOW WILL PERSIST. WRAPAROUND MOISTURE WILL BE FORCED UP THE MTNS

SUNDAY NIGHT WITH SOME REMAINING UPPER FORCING. THIS SHOULD RESULT

IN WIDESPREAD SNOW ALONG THE TN BORDER WITH THE POTENTIAL FOR

SEVERAL INCHES OF ACCUMULATION. WINDS ARE EXPECTED TO HOWL...TO THE

POINT THAT NEAR BLIZZARD CONDITIONS ARE NOT OUT OF THE QUESTION AT

TIMES LATE SUNDAY NIGHT OR EARLY MONDAY MORNING. A CONVEYOR BELT OF

LOW LEVEL MOISTURE DOWN FROM LAKE MICHIGAN WILL PERSIST THROUGH

MONDAY AND INTO MONDAY NIGHT. THE POTENTIAL FOR WINTER STORM

CONDITIONS WILL BE HIGHLIGHTED IN THE HWO. TEMPS WILL REMAIN WELL

BELOW NORMAL THRU THIS PART OF THE PERIOD.

This is after the 1 to 2 inches they said that might fall Sat. night. Party on my deck Sunday night!!!!

[Cheeznado]

you seem more optimistic than I remember?? You looking to go up to the mountains?

I may go to Boone Sunday morning, stay the night there and then go to Asheville Monday for a while before heading back. Depends on the models the next 48 hours- I would like to see at least 6" and strong winds.

[BullCityWx]

I may go to Boone Sunday morning, stay the night there and then go to Asheville Monday for a while before heading back. Depends on the models the next 48 hours- I would like to see at least 6" and strong winds.

There are certainly worse places to spend some time than Beer City USA(Asheville)

[Jon]

to the untrained/amateur folks like myself, i take it this is possibly a good sign....?

Don't know where you live but the simple answer: I guess it's a good sign...doesn't say too much, just confirms that there is a possibility of flurries on the backside of this thing east of the mountains in NC...NWS RAH has already picked up on this, as of 2:30 today:

FROM RAH:

VERY COLD AIR WILL BE CHASING THE BACK EDGE OF THE PRECIP

IMMEDIATELY BEHIND THE FRONT...AND THERE IS SOME POTENTIAL FOR A

CHANGEOVER OR MIX WITH SNOW SHWRS BY LATE SUNDAY AFT OR EARLY

EVENING...ESPECIALLY IN THE WEST...BUT REALLY NO CHANCE OF ANY

SNOW ACCUM AS ANY PRECIP WILL BE VERY LIGHT AND SHOWERY. TRIED TO

DEPCIT A FASTER THAN NORMALY DIURNAL DROP IN TEMPS LATE SUNDAY

BEHIND FRONT...BUT THIS WILL NEED TO BE ADJUSTED MORE PRECICELY AS

TIMING OF FRONT BECOMES MORE CLEAR. IF ANYTHING...MAY NEED TO BRING

COLDER TEMPS AND CHANGEOVER TO SOME SNOW SHWRS EVEN EARLIER

Basically if this thing slows, we could get cold air faster, means more frozen precip. But as for my area, Raleigh, I'm not excited.

[WeatherNC]

The NAM is looking at least a little interesting for me here in central NC. It looks like it's an all-out race between cold air and precip.... at hour 84 my 850 temp is below zero with .10-.25 precip falling. We'll see, I guess.

NAM outside of it's normally useful range which is about t-48hrs, so nothing to get excited at just yet... I would however, be surprised if we do not see a trend towards a cutoff at H5, passing in or near the upstate of SC over the next 24hrs worth of runs. The trough is just too deep and goes neg tilt over the FL Panhandle, that, in addition to the favorable jet structure, would argue for a close off imo. This is the 18z sim at 78hrs, likely to be way off from what actually happens, but verbatim everything falling to the west of that little void in central NC would be snow. Still a long shot, but these parcels are still in the data sparse Pac, and as currently progged, we are looking at a 180kt plus H2 jet, that will be screaming into WA state here in about 24hrs, and it wants to dig, as would the energy ahead of it.

and the H5 map @ 84

[neatlburbwthrguy]

Take 136 from Jasper over towards Dawsonville. You go up Burnt Mountain/Mt. Oglethorpe and they do pretty well in these situations. They usually get an inch when I see flurries at the house. The driving can be pretty dangerous though. I've had a couple of scary experiences up there.

Can I get there from Ga 400? Also, thanks for the heads up on the danger...I will be careful...

[burgertime]

NAM outside of it's normally useful range which is about t-48hrs, so nothing to get excited at just yet... I would however, be surprised if we do not see a trend towards a cutoff at H5, passing in or near the upstate of SC over the next 24hrs worth of runs. The trough is just too deep and goes neg tilt over the FL Panhandle, that, in addition to the favorable jet structure, would argue for a close off imo. This is the 18z sim at 78hrs, likely to be way off from what actually happens, but verbatim everything falling to the west of that little void in central NC would be snow. Still a long shot, but these parcels are still in the data sparse Pac, and as currently progged, we are looking at a 180kt plus H2 jet, that will be screaming into WA state here in about 24hrs, and it wants to dig, as would the energy ahead of it.

If this happened verbatim I would want to hit myself to sleep with a hammer as it would be just out of reach. Hopefully it can dig a little more and help us out in CLT.

[Gastonwxman]

Did anyone noticed how there seems to be a slug of moisture in the same spot on the 18z NAM at hr. 84 along the coast similar to that of the previous 18z GFS at hr. 102? Wonder if this run of the NAM's following it. Just thought I point that out.

[WeatherNC]

If this happened verbatim I would want to hit myself to sleep with a hammer as it would be just out of reach. Hopefully it can dig a little more and help us out in CLT.

And that remains to be seen, and like always, it is pretty close this run to something sig, which as eyewall's NC SN chances map points out, only counts in horseshoes and hand grenade exercises, not on prom night, and not on the 18z NAM at 78hrs... 0z run should be interesting, as the whole event is finally coming into the NAM's range, and imo, there is just too much energy at the base of that trough for a close off not to happen, given the encroaching jet. The 84hr graphic from Allan's site shows a secondary trying to form off the OBX, and what looks to be some banding associated with it around Lynchburg VA. Now, a little more digging, a little less influence with the PV energy in central Canada, and this low could form farther to the south along the baroclinic zone which is already established. Still a long shot, but a highly fluid amplification and vorticity pattern, which the guidance is still struggling to resolve...

p.s. Will be exiting the failboat dock left after this, and embarking on the failtrain for a one way trip to late Dec.

[burgertime]

Cold front is a little faster on 18z then it was on the 12z but it really doesn't change much. Guess it's all in the trends.

[Lookout]

im sorry i mis-worded my comment. however, i dont think you getting a dusting to half inch of snow is out of the question at this point...

Highly unlikely. It never works out for him or northeast Ga in general in post frontal/upslope snow situations.

18Z NAM trending slower and deeper......

Yeah the 18z nam is a little more interesting. Dropping the core of the coldest air straight over north Ga with plenty of 850mb humidity. There is even a little bit of 700mb humidity which means some decent cloud development. 18z nam would be better for flurries/snow showers...even a chance into northeast Ga. Accumulations will be nil though as I'm not impressed with the models..they aren't showing any 0.01 amounts anywhere in ga or at best barely touching the nc border counties. Normally if there is any chance of accumulation or really good coverage, the models will normally paint 0.01 in these situations. Considering that is not the case this time, I don't see it being a big deal...even though there is a chance flurries make it into northeast Ga which is of course unusual in these cases.

In should be noted the nam would suggest a few flurries possible into central Ga as well. In fact columbus and macon have a better shot than I do. (I hate downslope)

[NEGa]

im sorry i mis-worded my comment. however, i dont think you getting a dusting to half inch of snow is out of the question at this point...

I usually get downsloped it's rare for this set up to work imby. Has to be extreme cold and pretty decent moisture to overcome downslope

One can hope, guess we will be floodlighting it again!

Yep lol. I really haven't seen flurries yet and even in bad years i usually have seen some flakes by now so I am getting impatient

Highly unlikely. It never works out for him or northeast Ga in general in post frontal/upslope snow situations.

Sigh - yep see above lol. The worst part is i can see the snow falling fast and furious the other side of the valley about 10 - 15 miles away. Talk about being smacked around by mother nature and slapped silly

[eyewall]

I usually get downsloped it's rare for this set up to work imby. Has to be extreme cold and pretty decent moisture to overcome downslope

Yep lol. I really haven't seen flurries yet and even in bad years i usually have seen some flakes by now so I am getting impatient

Sigh - yep see above lol. The worst part is i can see the snow falling fast and furious the other side of the valley about 10 - 15 miles away. Talk about being smacked around by mother nature and slapped silly

At least you can drive that 10 miles and be in it .

[NEGa]

At least you can drive that 10 miles and be in it .

Yes, but the good ones seem to happen mon - fri during working hours. Lol. I wake up, look out and see all the snow, then have to head out to the office

[Psalm 148:8]

Found this on another board....kudos to the poster CT on the find.....What say ye?

AREA FORECAST DISCUSSION

NATIONAL WEATHER SERVICE QUAD CITIES IA IL

315 PM CST THU DEC 9 2010

".LONG TERM...THURSDAY NIGHT THROUGH NEXT WEDNESDAY...

...SHARPLY COLDER LATE SATURDAY WITH MINOR SNOW AMOUNTS...THEN WINDY

WITH FRIGID WIND CHILLS INTO TUESDAY...

COMMENT...MAJOR CHANGES HAVE OCCURRED THE PAST 24 HRS OF RUNS WITH

FURTHER LATENT HEAT DRIVEN CHANGES EXPECTED. THE EVENT THIS WEEKEND

IS HIGHLY NON-LINEAR WHICH MODELS BY THE IMPRESSIVE DYNAMICS ARE

HAVING SIGNIFICANT PROBLEMS WITH. MAIN SFC LOW TO PASS MAINLY NORTH

OR NORTH OF AREA WITH INTENSE BACKSIDE ENERGY TO PHASE INTO SYSTEM

SATURDAY NIGHT INTO SUNDAY EVENING. THIS IS 300 TO 400 MILES FURTHER

NORTH THAN SUITE OF SOLUTIONS JUST 24 TO 30 HOURS AGO. THIS EVENT

WILL LEAD TO A 3 TO 4 SIGMA STRONG STORM SYSTEM ON EAST COAST BY LATE

SUNDAY. MUCH OF THIS SAME ENERGY WILL FIND ITS WAY INTO EUROPE BY DAY

6...LASTING INTO DAY 12 WITH CONTINUED IMPRESSIVE COLD STILL ON TAP

THERE PER YESTERDAY/S AFTERNOON DISCUSSION. THE PHASING OF LATENT

HEAT ENERGY IS ONE OF THE MOST UNUSUAL ASPECTS OF THIS SYSTEM...IT

WILL GO INTO THIS FORECASTER/S ARCHIVE FOR FURTHER STUDY/REFERENCE.

THE MODEL RUN TO RUN CHANGES ON ALL SOLUTIONS ARE SOME OF THE LARGEST

RECENTLY SEEN IN 12 TO 24 HOURS. NOT SURPRISING FOR A DEVELOPING 3

TO 4 PLUS SIGMA EVENT WHICH BY DEFINITION IS ROUGHLY A 1 IN 100...UP

TO OVER 1 IN 1000 PLUS PERCENTAGE PHENOMENA WHICH MODELS AREN/T

EXPLICITLY DESIGNED FOR.

OVERVIEW...MODEL INITIALIZATION AND VERIFICATION ADEQUATE WITH LATENT

HEAT TRENDS PER VERIFICATION SUPPORT USING A MIX OF NAM-WRF AND HI-

RES ECMWF INTO SATURDAY NIGHT. THEN SUNDAY ON...WENT WITH A 60/40

BLEND OF GFS AND HI-RES ECMWF INTO NEXT WEDNESDAY. MAJOR CHANGES

CONTINUE WITH VERY DYNAMIC SYSTEM WHICH SHOULD CONTINUE INTO TONIGHT

PRECLUDING BELOW AVERAGE CONFIDENCE IN SURFACE TRACK AND EVOLUTION.

TRENDS SUGGEST BACKSIDE ENERGY TO PRODUCE LOTS OF WIND AND LIGHT TO

POSSIBLY MODERATE SNOW TOTALS WITH SOME BLOWING SNOW SATURDAY NIGHT

POSSIBLE INTO SUNDAY FOR LATER SHIFTS TO FURTHER EVALUATE WITH MORE

WARMING AHEAD OF FRONT UNTIL LATE SATURDAY AFTERNOON."

[oconeexman]

I find this odd considering GSP usually takes the conservative route this far out.

Sunday: Rain before 3pm, then a slight chance of rain and snow showers between 3pm and 4pm, then a slight chance of snow showers after 4pm.

[WeatherNC]

Found this on another board....kudos to the poster CT on the find.....What say ye?

AREA FORECAST DISCUSSION

NATIONAL WEATHER SERVICE QUAD CITIES IA IL

315 PM CST THU DEC 9 2010

".LONG TERM...THURSDAY NIGHT THROUGH NEXT WEDNESDAY...

...SHARPLY COLDER LATE SATURDAY WITH MINOR SNOW AMOUNTS...THEN WINDY

WITH FRIGID WIND CHILLS INTO TUESDAY...

COMMENT...MAJOR CHANGES HAVE OCCURRED THE PAST 24 HRS OF RUNS WITH

FURTHER LATENT HEAT DRIVEN CHANGES EXPECTED. THE EVENT THIS WEEKEND

IS HIGHLY NON-LINEAR WHICH MODELS BY THE IMPRESSIVE DYNAMICS ARE

HAVING SIGNIFICANT PROBLEMS WITH. MAIN SFC LOW TO PASS MAINLY NORTH

OR NORTH OF AREA WITH INTENSE BACKSIDE ENERGY TO PHASE INTO SYSTEM

SATURDAY NIGHT INTO SUNDAY EVENING. THIS IS 300 TO 400 MILES FURTHER

NORTH THAN SUITE OF SOLUTIONS JUST 24 TO 30 HOURS AGO. THIS EVENT

WILL LEAD TO A 3 TO 4 SIGMA STRONG STORM SYSTEM ON EAST COAST BY LATE

SUNDAY. MUCH OF THIS SAME ENERGY WILL FIND ITS WAY INTO EUROPE BY DAY

6...LASTING INTO DAY 12 WITH CONTINUED IMPRESSIVE COLD STILL ON TAP

THERE PER YESTERDAY/S AFTERNOON DISCUSSION. THE PHASING OF LATENT

HEAT ENERGY IS ONE OF THE MOST UNUSUAL ASPECTS OF THIS SYSTEM...IT

WILL GO INTO THIS FORECASTER/S ARCHIVE FOR FURTHER STUDY/REFERENCE.

THE MODEL RUN TO RUN CHANGES ON ALL SOLUTIONS ARE SOME OF THE LARGEST

RECENTLY SEEN IN 12 TO 24 HOURS. NOT SURPRISING FOR A DEVELOPING 3

TO 4 PLUS SIGMA EVENT WHICH BY DEFINITION IS ROUGHLY A 1 IN 100...UP

TO OVER 1 IN 1000 PLUS PERCENTAGE PHENOMENA WHICH MODELS AREN/T

EXPLICITLY DESIGNED FOR.

OVERVIEW...MODEL INITIALIZATION AND VERIFICATION ADEQUATE WITH LATENT

HEAT TRENDS PER VERIFICATION SUPPORT USING A MIX OF NAM-WRF AND HI-

RES ECMWF INTO SATURDAY NIGHT. THEN SUNDAY ON...WENT WITH A 60/40

BLEND OF GFS AND HI-RES ECMWF INTO NEXT WEDNESDAY. MAJOR CHANGES

CONTINUE WITH VERY DYNAMIC SYSTEM WHICH SHOULD CONTINUE INTO TONIGHT

PRECLUDING BELOW AVERAGE CONFIDENCE IN SURFACE TRACK AND EVOLUTION.

TRENDS SUGGEST BACKSIDE ENERGY TO PRODUCE LOTS OF WIND AND LIGHT TO

POSSIBLY MODERATE SNOW TOTALS WITH SOME BLOWING SNOW SATURDAY NIGHT

POSSIBLE INTO SUNDAY FOR LATER SHIFTS TO FURTHER EVALUATE WITH MORE

WARMING AHEAD OF FRONT UNTIL LATE SATURDAY AFTERNOON."

One of the better finds in recent memory Psalm!!! Thanks for sharing and no doubt the most interesting disco thus far on this event. Noted a couple WFO's brushing off the 12z EC yesterday referencing latent heat feedback, not sure of the accuracy in that as I have no clue as to the initialization parameters of the models, and algorithms used to calculate such. For those who do not know what latent heat is, and it's implifications on the physical systems around us, this is a great article explaining the process...

A complete understanding of latent heat will add greatly to your analysis and forecasting skills. Latent heat is nothing magical but can be very confusing to understand. Water molecules can move in three ways. They can move by vibration, rotation, and translation. Ice is not very free to move. Ice can vibrate but ice remains rigid. Liquid water moves freely but since the molecules are still very close together they do not move as freely as air.

Solid water (ice) is the most ordered state of H20 while gas is the least ordered. In order for ice to go from an ice to a liquid state, energy must be added to cause the ice to go from a higher state to a lower ordered state. When ice melts or water evaporates, energy must be taken from the environment in order for the ice or liquid to move to a less ordered state. Energy is needed to weaken the individual hydrogen bonds between H20 molecules. When water (in any of the three phrases) moves from a higher to a lower ordered state, the air surrounding the H20 will have heat subtracted from it. The three processes that subtract heat from the surrounding air are evaporation, melting and sublimation (solid to gas). When water (in any of the three phrases) moves from a lower to a higher ordered state, the air surrounding the H20 will have energy added to it. This is called a release of latent heat (e.g. when heat is subtracted from liquid water, the individual water molecules will slow down. They eventually slow down to the point at which the hydrogen bonds do not allow the liquid to rotate anymore. Ice now develops. The energy the water molecules once had to rotate has been given up to the surrounding air). The three processes that add heat to the surrounding air are condensation, freezing and deposition (gas to solid).

IMPORTANT: the processes of evaporation and condensation take 7.5 times as much energy as melting or freezing. This is why evaporational cooling will cool the air much more than the melting of snow. For example, let's say snow is falling and the outside temperature is 40 degrees Fahrenheit. As the snow falls into the warmer air it will begin to melt and some of it will be evaporating. The evaporation from the wet snow will cool the air 7.5 times as much as the melting of the snow. If the temperature drops from 40 to 32 degrees as the snow falls, about 7 of those 8 degrees of cooling is caused by the evaporation process. Melting cools the air also, just not near as much as evaporation does. When water undergoes a phase change (a change from solid, liquid or gas to another phase) the temperature of the H20 stays at the same temperature. Why? Energy is being used to either weaken the hydrogen bonds between H20 molecules or energy is being taken away from the H20 which tightens the hydrogen bonds. When ice melts, energy is being taken from the environment and absorbed into the ice to loosen the hydrogen bonds. The energy taken to loosen the hydrogen bonds causes the surrounding air to cool (energy is taken away from the environment: this is latent heat absorption). The temperature of the melting ice however stays the same until all the ice is melted. All hydrogen bonds must be broken from the solid state before energy can be used to increase the H20's temperature.

Energy always flows from a warmer object toward a colder object. An ice cube at 32 degrees F absorbs energy from air that has a temperature warmer than freezing. Energy flows from the room toward the ice cube. Throw enough ice cubes in your kitchen and you may notice the temperature of the air cooling slightly. Energy is taken from your warmer room and moved into the ice cubes to melt them; A subtraction of energy causes cooling. The same holds when comparing freezing to condensation. The condensation process will warm the surrounding air 7.5 times as much as when the freezing process occurs. When a thunderstorm develops, the release of latent heat by condensation is 7.5 times as much as the release of latent heat by freezing. Now let's do some application of this latent heat process with regard to forecasting.

1. Evaporational cooling from rain (in the absence of downdrafts) will cause the temperature to decrease but the dewpoint to increase. The dewpoint will always (in the range of normally observed temperatures) increase more than the temperature falls (e.g. suppose the temperature is 70 F with a dewpoint of 50 F, after a persistent rain the temperature will cool to about 63 and the dewpoint will rise to about 63).

2. Temperatures have a difficulty warming significantly on days when there is surface snow cover. The melting and evaporation from the snow continuously cools the air.

3. Condensation releases latent heat. This causes the temperature of a cloud to be warmer than it otherwise would have been if it did not release latent heat. Anytime a cloud is warmer than the surrounding environmental air, it will continue to rise and develop. The more moisture a cloud contains, the more potential it has to release latent heat.

4. The amount of cooling experienced during melting or evaporation is a function of the dewpoint depression. If the air is saturated, evaporation will be minimized. Evaporational cooling can not take place once dew forms on the ground but can start to take place when the sun begins to warm the surface (dewpoint depression becomes greater than 0).

5. Dry climates tend to have a larger diurnal range in temperature than moist climates. The primary reason is because of latent heat. In a dry climate, evaporational cooling is at a minimum and there is little water vapor to trap longwave radiation at night. Therefore, in a dry climate the highs will be higher and the lows lower as compared to a moist climate at the same altitude and latitude (all else being equal).

a little less complex then what we learned in P-chem, but for most it should be either a refresher, or basic grasp on the subject

http://www.theweatherprediction.com/habyhints/19/

[Marion_NC_WX]

The 18z GFS numerical data on the metostar site trended significantly colder in terms of the cold air advection and the resultant low temps Monday and Tuesday Mornings...850 temps at the peak of the CAA is -18 for about 12 straight hours and the guidance shows a temp of 4 degrees at 12z Tues.

BTW, it also shows about .20 qpf for the Thursday timeframe in which it could be of the frozen variety.

http://wxweb.meteost...shtml?text=KMRN

[Wild Weather Monger]

Yes, I know. It's the JMA. Couldn't help myself given the placement of the low on this run.