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Jan 25th Winter Weather Discussion Thread


Marion_NC_WX

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18z NAM with energy in northern CA & NV at 42hrs, compared to northern MT at 12z, this should be an interesting run.

Good to hear from you!

People saying this winter is as bad as last are crazy, this is the 2nd credible threat within one week for us to follow! The first potent clipper to reach outside the mountains in years!

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A note about the dry air..... the modeling should account for the dry air with the precip amounts. Now, any model could certainly under-estimate the amount of dry air (and they often do), but the modeling does account for evaporation in the QPF amounts.

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Yeah, the southern parcel went 'poof' as burger would say

I still see it... IDK if we're talking about the same thing here. We're probably going to get a phase, not sure where this things gonna end up this run.

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RAH afternoon thoughts:

 

...POTENTIAL WINTERY MIX FRIDAY INTO FRIDAY NIGHT...THURSDAY AND THURSDAY NIGHT:REINFORCEMENT OF ARCTIC AIR INTO THE CAROLINAS WILL ENSUE ONTHURSDAY IN THE WAKE OF CANADIAN SHORTWAVE TROUGH EXITING THEMID-ATLANTIC SEABOARD AND ON THE HEELS OF A STRONG ~1040MBOVER THE UPPER MIDWEST BUILDING SOUTHEASTWARD INTO THE MID-ATLANTICAND CAROLINAS. UNDER FULL SUNSHINE...TEMPERATURES WILL STRUGGLE TO CLIMB OUTOF THE 30S ON THURSDAY WITH GRADIENT NORTHERLY WINDS OF 10 TO 20 MPHPROVIDING AN ADDED NIP TO THE AIR. TEMPERATURES WILL DROP ABRUPTLYAFTER SUNSET WITH STRONG RADIATIONAL COOLING EXPECTED AS THE ARCTICHIGH BUILDS DIRECTLY OVERHEAD. SUB-FREEZING LOWS WELL INTO THE LOWERTO MID 20S.FRIDAY AND FRIDAY NIGHT:A VERY COMPLEX SYNOPTIC IS FORECAST BY THE MODELS AS SECONDARY LOWDEVELOPS INVOF THE LOWER MS VALLEY SPINS UP IN RESPONSE TO DIGGINGPACIFIC NW ENERGY INTO THE CENTRAL US...LEADING TO AN EXPANDINGSHIELD OF PRECIP UPSTREAM. THIS SECONDARY LOW WILL LIE ON THESOUTHERN PERIPHERY OF THE PRIMARY NORTHERN STREAM LOW AND COLD FRONTOVER THE UPPER MIDWEST/GREAT LAKES REGION. THE WAVY FRONTAL ZONE ISTHEN FORECAST TO PROGRESS EAST THROUGH THE MID-ATLANTICREGION...CONSOLIDATING/MERGING ALONG THE WAY BEFORE A CENTRALIZEDLOW EMERGES OFF THE MID-ATLANTIC COAST.THE SUBFREEZING ANTECEDENT CONDITIONS AHEAD OF THE LOW/FRONTAPPROACH FAVORS NARROW CORRIDORS OF FREEZING AND FROZEN PRECIPITATIONACROSS NORTH CAROLINA. MOISTURE IS ACTUALLY FAIRLY SHALLOW WITH WARMADVECTION PROCESSES(SHOWERY LIKE) DRIVING THE PRECIP WITH DYNAMICFORCING/LIFT WEAK TO NEGLIGIBLE COMPARED TO LAST WEEKS STORM SYSTEM.BUT THERE HAS DEFINITELY BEEN A MODEL TREND TO MUCH COLDER THERMALPROFILES(ESPECIALLY IN BOUNDARY LAYER TEMPERATURES)ACROSS THE ENTIRECWA WITH SFC DEWPOINTS IN THE SINGLE DIGITS TO TEENS AS PRECIP MOVESIN...LOCKING IN THE SUB-FREEZING TEMPERATURES OVER THE FAVOREDPIEDMONT DAMMING REGION AND POSSIBLY TO EVEN NEAR FREEZING AS FAREAST AS THE SANDHILLS/I95 CORRIDOR. WHILE TIMING/AMOUNTS ARE STILLSOMEWHAT UNCLEAR BASED ON THE LARGE SOLUTION SPREAD....THE ANOMALOUSANTECEDENT ARCTIC AIRMASS IN PLACE WILL RESULT IN THE INTRODUCTIONOF BOTH FROZEN AND FREEZING PRECIP WITH MORE IN THE WAY OF FROZENPRECIP IN THE WESTERN/CENTRAL PIEDMONT(HEART OF THE DAMMING REGION...TRENDING TO A VERY COLD RAIN ACROSS THE SOUTHEAST(ALTHOUGH IT COULDBE A MIX AT THE ONSET). SOMEWHERE IN BETWEEN WILL POTENTIALLYLIE A NARROW CORRIDOR OF FREEZING RAIN OR SNOW/SLEET/FREEZING RAINMIX (DUE TO LIMITED SATURATION ALOFT)EVERYONE IS ADVISED TO MONITOR THE LATEST FORECAST AND POTENTIALWATCHES AND WARNINGS OR ADVISORIES THAT WILL LIKELY FOLLOW IN THENEXT 24 TO 48 HOURS AS THIS COMPLEX EVENT UNFOLDS.
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A note about the dry air..... the modeling should account for the dry air with the precip amounts. Now, any model could certainly under-estimate the amount of dry air (and they often do), but the modeling does account for evaporation in the QPF amounts.

 

This is what I've been told. The thing the models don't do a good job of though is temperatures dropping at the surface due to evaparotional cooling. The 18z nam for example has some light precip with temps essentially staying the same....which is virtually impossible with temps in the upper 20s/low 30s in north ga and dewpoints in the teens with a deep and cold  boundary layer. Even light precip would cause temps to drop easily with that.

 

Now IF it was a very shallow cold layer...say only up to 975mb and strong waa aloft, you can have temps in the low 30s/dewpoints in the teens when the precip starts but due to the shallow nature of the cold air it mixes out and temps won't drop. Been burnt on that before. Essentially what I'm saying is you have to have a certain depth to along with the cold air at the surface from my experience.

Not worried right now. It's the NAM and plenty of time for the qpf to come back the other way.

Worrying about what the 18z nam is showing is silly.

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Afternoon discussion out of GSP:

 

THERE IS
SOME QUESTION AS TO WHETHER THE ADVANCING LOW WILL BE ABLE TO BUDGE
HIGH PRESSURE OVER THE ERN SEABOARD...WHICH COULD KEEP US UNDER A
WEDGE OF COLD AIR. GFS AND NAM SEEM TO THINK THE CAD WILL ERODE
DURING THE DAY FRI. HAVE TENTATIVELY GONE WITH HIGH TEMPS THAT
REFLECT THAT. PRECIP TYPE DOES BEGIN AS A WINTRY MIX OVER MAINLY NC
GIVEN SUBFREEZING TEMPS THERE FRI MORNING.  IF THE WARM AIR IS ABLE
TO PUSH NORTH MOST AREAS WILL CHANGE TO RAIN.  THE AREAS THAT DO SEE
FROZEN PRECIP ARE EXPECTED TO SEE MOSTLY FREEZING RAIN WITH THE
MOISTURE BEING CONCENTRATED NEAR THE GROUND...SIMILAR TO THE THU
EVENT.

 

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