CAD_Wedge_NC Posted February 16, 2015 Share Posted February 16, 2015 Amateur question: How do wet-bulb temperatures affect what's going to happen (as I see many discussing wet-bulb temps). It will give you an idea of what the temperatures will look like after the atmosphere saturates. Link to comment Share on other sites More sharing options...
airmarci Posted February 16, 2015 Share Posted February 16, 2015 Amateur question: How do wet-bulb temperatures affect what's going to happen (as I see many discussing wet-bulb temps). It's the minimum temperature that a theoretical parcel of air would cool to due by way of evaporation/sublimation of precipitation. If the wet bulb temperature is higher then it will typically take less time for the atmosphere to saturate and precipitation to start reaching the ground. Link to comment Share on other sites More sharing options...
wxduncan Posted February 16, 2015 Share Posted February 16, 2015 000 FXUS62 KGSP 161806 AFDGSP AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC 106 PM EST MON FEB 16 2015 .SYNOPSIS... A MOIST LOW PRESSURE SYSTEM WITH WIDESPREAD WINTRY PRECIPITATION WILL TRACK ACROSS THE CAROLINAS TONIGHT AND MOVE OFF THE MID ATLANTIC COAST TUESDAY MORNING. IN ITS WAKE...AN ARCTIC COLD FRONT WILL SWEEP THROUGH FROM THE NORTH WEDNESDAY. VERY COLD HIGH PRESSURE WILL THEN BUILD IN AND PERSIST THROUGH FRIDAY...BEFORE A MOIST SURFACE BOUNDARY MOVES INTO THE AREA OVER THE WEEKEND. && .NEAR TERM /THROUGH TUESDAY/... AS OF 1255 PM EST...THE UPPER LEVEL SHORTWAVE MOVING FROM THE SRN PLAINS TO THE MID MS RIVER VALLEY TODAY WILL DAMPEN AS IT MOVES EASTWARD ACROSS THE APPALACHIANS LATER TONIGHT. THE ASSOCIATED SFC LOW CENTER MOVING ACROSS THE DEEP SOUTH SHOULD TRACK FROM THE CENTRAL AL/GA BORDER AT 00Z THIS EVENING...TO NW OF AUGUSTA GA BY 06Z...TO OFF THE OUTER BANKS OF NC BY 12Z TUE. AHEAD OF THIS LOW...PRECIPITATION IS RAPIDLY FILLING IN FROM THE WEST THIS AFTN...AND THERMAL PROFILES ARE QUICKLY WET BULBING DOWN TO SUPPORT MAINLY SNOW/SLEET SHORTLY AFTER ONSET. THE DEEPER FORCING WILL REACH THE FORECAST AREA FROM THE W STEADILY THROUGH THE LATE AFTN HOURS...MAXIMIZING 00Z TO 03Z AS THE BEST SRLY JET TRAVERSES THE REGION. THE LATEST RAP RUN HAS REGAINED IT/S THERMAL SANITY SOMEWHAT...WITH SUBFREEZING SFC TEMPS NOW LARGELY LOCKED IN ALONG AND NW OF INTERSTATE 85 UNTIL MID TO LATE EVENING. THE MAIN EXCEPTION WILL BE IN WRN/SRN UPSTATE SECTIONS AS WELL AS NE GA OUTSIDE OF THE MTNS...WHERE THE SREF MEAN/GEFS ALSO SUPPORT EARLIER WARMING OF SFC TEMPS. THIS WILL MAKE FOR A VERY SHARP ICE ACCUM GRADIENT IN THE SRN TIER...BUT THE CURRENT HAZARD SUITE SEEMS TO HAVE THIS FAIRLY WELL PLACED. LOCATIONS NW OF INTERSTATE 40 LOOK TO BE MORE SOLIDLY SNOW THROUGHOUT THE VAST MAJORITY OF THE EVENT...WITH SOME SLEET ONLY MIXING IN AT TIMES EARLY AND LATE...AND ANY FZRA WINDOW FAIRLY BRIEF. NRN BLUE RIDGE AREA SNOW ACCUMS HAVE BEEN BOOSTED SLIGHTLY. EXPECT SOME DRY SLOTTING TO ARRIVE AT MID LEVELS CIRCA 06Z TO 09Z...WITH POPS TRENDING DOWN WEST TO EAST LATE TONIGHT. NW FLOW MOISTURE WILL DIMISH ALONG THE SPINE OF THE SRN APPALACHIANS TUE MORNING...WITH LOW LEVEL FLOW BACKING AHEAD OF THE FALLING HEIGHTS TO THE W AS A DEEP CENTRAL CONUS TROUGH TRANSITIONS EWD. MELTING IS LIKELY IN THE SRN MTNS AND ACROSS THE FOOTHILLS/PIEDMONT TUE AFTN...TEMPS REBOUNDING ABOVE FREEZING IN WEAK WESTERLY DOWNSLOPE FLOW. && Link to comment Share on other sites More sharing options...
superjames1992 Posted February 16, 2015 Share Posted February 16, 2015 FWIW, the Euro did come in a little south/wetter. 0.6" QPF for many, which is on the lower end of the guidance, but a little more than last night's run. Link to comment Share on other sites More sharing options...
strongwxnc Posted February 16, 2015 Share Posted February 16, 2015 James, how much is it worth at this point? Serious question... FWIW, the Euro did come in a little south/wetter. Link to comment Share on other sites More sharing options...
superjames1992 Posted February 16, 2015 Share Posted February 16, 2015 James, how much is it worth at this point? Serious question... Mainly, it just gives us more precip, though still on the lower end of guidance. It probably starts you out as a little snow. Looks like my area might get an inch or two before going over to sleet. Interestingly, 850s never get above 1C here, which is lower than the last few runs. Your area, CLT, and RDU are all below freezing for the duration. Looks like low 20s/upper 10s here. It mostly has the GSP area too warm for ZR (32/33), but the Euro is supposedly warm-biased at 2m in CAD situations, so who knows about that. Link to comment Share on other sites More sharing options...
Berlin1926 Posted February 16, 2015 Share Posted February 16, 2015 based on radar trends i think rdu has a good shot of seeing an initial 1" of snow before changeover to sleet. snowing already in roxboro and continuing to move south. hrrr has been way off based on radar. Correction...it was snowing in Roxboro for about 10 minutes. Link to comment Share on other sites More sharing options...
griteater Posted February 16, 2015 Share Posted February 16, 2015 I'd say this looks reasonable in terms of radar progression - http://mp1.met.psu.edu/~fxg1/NAMSFC4SE_12z/rloop.html Link to comment Share on other sites More sharing options...
griteater Posted February 16, 2015 Share Posted February 16, 2015 Right now it has Charlotte on the warm side of the boundary unfortunately which means primarily rain. Greenville, SC is literally on the edge between substantial frozen precipitation and more of a nuisance variety per HRRR. Hickory is entrenched in the cold sector and will probably go Snow/Sleet for the duration of the precipitation. This will fail Link to comment Share on other sites More sharing options...
superjames1992 Posted February 16, 2015 Share Posted February 16, 2015 The latest RAP has good precip moving into the Western Piedmont and foothills by 4 or 5 PM. It kind of hits a wall, though, and doesn't advance much further after that for a few hours. The latest HRRR agrees. Precip makes it to GSO by hr 3, but doesn't advance to Burlington until hr 6. We'll see about that. Link to comment Share on other sites More sharing options...
phil882 Posted February 16, 2015 Share Posted February 16, 2015 This will fail We shall see... right now if I were in Greenville, SC I'd be very worried from a potential crippling ice storm. HRRR soundings strongly support primarily freezing rain when the heavier precip arrives. http://www.atmos.albany.edu/student/ppapin/lb13_img/hrrr/hrrr_ncep_snd_gsp.php Latest HRRR shows Charlotte very much in the same situation... huge warm nose, but below freezing in the lowest 25-50 hPa http://www.atmos.albany.edu/student/ppapin/lb13_img/hrrr/hrrr_ncep_snd_clt.php Link to comment Share on other sites More sharing options...
strongwxnc Posted February 16, 2015 Share Posted February 16, 2015 RAP also keep the surface and 850 below 32 in my area. The latest RAP has good precip moving into the Western Piedmont and foothills by 4 or 5 PM. Link to comment Share on other sites More sharing options...
wxduncan Posted February 16, 2015 Share Posted February 16, 2015 The latest RAP has good precip moving into the Western Piedmont and foothills by 4 or 5 PM. It kind of hits a wall, though, and doesn't advance much further after that for a few hours. The latest HRRR agrees. Precip makes it to GSO by hr 3, but doesn't advance to Burlington until hr 6. Longer duration then for us? Link to comment Share on other sites More sharing options...
superjames1992 Posted February 16, 2015 Share Posted February 16, 2015 RAP also keep the surface and 850 below 32 in my area. Yep, looks like it would change us over from snow around 9 or 10 PM tonight, though I don't really trust the RAP that far out. Link to comment Share on other sites More sharing options...
strongwxnc Posted February 16, 2015 Share Posted February 16, 2015 RAP has the temps backing down to 29 in this area after hour 4. Just need some strong returns to head over right now. Yep, looks like it would change us over around 9 or 10 PM tonight, though I don't really trust the RAP that far out. Link to comment Share on other sites More sharing options...
griteater Posted February 16, 2015 Share Posted February 16, 2015 Latest HRRR shows Charlotte very much in the same situation... huge warm nose, but below freezing in the lowest 25-50 hPa Agree on freezing rain, but not rain Link to comment Share on other sites More sharing options...
superjames1992 Posted February 16, 2015 Share Posted February 16, 2015 The latest SREF plumes look about the same. Maybe a little more snow here on the mean (over 1"). QPF is largely the same as the SREF mean has reflected these totals for about three runs now. It is right in the middle of the model consensus QPF for the most part, so these are probably realistic QPF outputs to expect for these areas. QPF: GSO: ~0.8" CLT: ~0.65" RDU: ~0.75" GSP: ~0.9" MWK: ~0.8" HKY: ~0.75" AVL: ~1.0" The 18z NAM should be out soon, as well, as we get to zero hour. EDIT: One big change. P-type pops for freezing rain are considerably down here. Not surprising. It has snow as the most likely P-type until about 02z or 03z. Link to comment Share on other sites More sharing options...
griteater Posted February 16, 2015 Share Posted February 16, 2015 superjames, do you have the strength to hold off this warm advection at 850mb, lol? Link to comment Share on other sites More sharing options...
superjames1992 Posted February 16, 2015 Share Posted February 16, 2015 superjames, do you have the strength to hold off this warm advection at 850mb, lol? No, but just give us some heavy precip as the warmer mid-levels surge northward so we can get some good snowfall rates before the changeover. It seems that in past experience in these situations, snowfall rates are pretty awesome right before we go over to sleet with all the lift. Link to comment Share on other sites More sharing options...
Smoked Posted February 16, 2015 Share Posted February 16, 2015 The southward trend in low position might be related to the magnitude of the cold air at the surface which models continue carry a warm bias. I think the actual track will trend a bit further south then current models suggest. Link to comment Share on other sites More sharing options...
Extreme NEGA Posted February 16, 2015 Share Posted February 16, 2015 Good afternoon everyone. This is my first post on here. I hope to keep you guys informed on what's headed for the upstate of SC in the future. Right now it's 32 and dropping in Toccoa with freezing rain. It was 38 when the Precip first started. Starting to wonder if it will warm up here like they say as the bulk of the precip gets here this afternoon. Link to comment Share on other sites More sharing options...
superjames1992 Posted February 16, 2015 Share Posted February 16, 2015 Comparing hr 3 of the 18z NAM and hr 9 of the 12z NAM, you can see that this run is a little colder for the CAD regions. Maybe 25 miles S at 850 mb. Not sure how that will develop going forward or if it even means anything at this point in the game. Link to comment Share on other sites More sharing options...
griteater Posted February 16, 2015 Share Posted February 16, 2015 Wanted to see if someone could help with this question... It seems like to me that wedging east of the mountains would enhance the amount of warm air advection as the enhanced 850mb flow approaches. That is, the temperature gradient is strongest their across the cold air damming boundary. My question is, if warm air advection is enhanced there (an assumption I'm making), why don't the areas east of the mtns in NC typically see enhanced precip in that region. Is there something else counteracting this mechanism, like maybe the drier profiles aloft? I wouldn't think there would be much in the way of downsloping in this setup (another potential mechanism to counter enhanced precip). Link to comment Share on other sites More sharing options...
btownheel Posted February 16, 2015 Share Posted February 16, 2015 The southward trend in low position might be related to the magnitude of the cold air at the surface which models continue carry a warm bias. I think the actual track will trend a bit further south then current models suggest. From my amateur perspective, that would be good for most NC folks correct? Limit the WWA on the NW side of the LP and keep the CAD locked in? Link to comment Share on other sites More sharing options...
drfranklin Posted February 16, 2015 Share Posted February 16, 2015 We shall see... right now if I were in Greenville, SC I'd be very worried from a potential crippling ice storm. HRRR soundings strongly support primarily freezing rain when the heavier precip arrives. http://www.atmos.albany.edu/student/ppapin/lb13_img/hrrr/hrrr_ncep_snd_gsp.php Latest HRRR shows Charlotte very much in the same situation... huge warm nose, but below freezing in the lowest 25-50 hPa http://www.atmos.albany.edu/student/ppapin/lb13_img/hrrr/hrrr_ncep_snd_clt.php seeing icicles form here Link to comment Share on other sites More sharing options...
downeastnc Posted February 16, 2015 Share Posted February 16, 2015 MHX finally wised up and upgraded Pitt Co to a winter storm warning if this verifies its gonna get nasty......surfaces here have been sub freezing ( and not just barely its been well below freezing) for 40 hrs straight now...... that's UNREAL and unheard of leading up to a winter weather event in eastern NC..... Call by MHX for us up to a inch of sleet and a .50" ice ugh.... * ACCUMULATIONS...SNOW AND SLEET MAY ACCUMULATE UP TO 1 INCH WITH A QUARTER TO UP TO A HALF OF AN INCH OF ICE ACCRUAL. HIGHEST AMOUNTS NORTH AND WEST OF A KINSTON...WASHINGTON...CRESWELL LINE.* IMPACTS...ROADS WILL QUICKLY BECOME SNOW...SLEET...AND ICE COVERED AND TRAVEL WILL BECOME DANGEROUS. FREEZING RAIN ACCRUAL ON TREES AND POWERLINES MAY ALSO RESULT IN SCATTERED TO NUMEROUS POWER OUTAGES. Link to comment Share on other sites More sharing options...
SnowDeac Posted February 16, 2015 Share Posted February 16, 2015 Haven't seen this question posed. Once sleet begins, does that indicate the warm nose has arrived (and in this case is here to stay)? Or can heavier precip rates/saturation of the column cause the precip to go back to snow? Link to comment Share on other sites More sharing options...
Solak Posted February 16, 2015 Share Posted February 16, 2015 .NEAR TERM /THROUGH TUESDAY/... AS OF 300 PM MONDAY... ...POTENTIAL FOR CRIPPLING ICE STORM INCREASING TONIGHT... ...WINTER STORM WARNINGS AND WINTER WEATHER ADVISORY REMAIN IN EFFECT... OVERVIEW: SHORTWAVE ENERGY TRACKING ACROSS THE CENTRAL MS RIVER VALLEY THIS AFTERNOON WILL PROGRESS INTO THE CAROLINAS AND MID- ATLANTIC TONIGHT. AN ATTENDANT SFC LOW WILL STRENGTHEN AS IT TRACKS EAST ACROSS THE DEEP SOUTH THIS AFTERNOON...THEN ENE ACROSS COASTAL PORTIONS OF THE CAROLINAS TONIGHT. PRECIP CHANCES/AMOUNTS: INCREASING FROM WEST/SW THIS AFTERNOON... INCREASING TO NEAR 100% EVERYWHERE BETWEEN SUNSET AND MIDNIGHT... REMAINING ~100% OVERNIGHT...THEN ENDING FROM WEST-EAST 09-15Z TUE MORNING. STORM TOTAL LIQUID EQUIV PRECIP AMOUNTS ARE EXPECTED TO RANGE FROM 0.50-1.00". PRECIP TYPE/ACCUM: AN ATYPICALLY COLD/DRY ANTECEDENT AIRMASS AND A PROGRESSIVE SHORTWAVE TROUGH /ATTENDANT SFC CYCLONE/ TRACKING JUST SOUTH OF THE REGION WILL SET THE STAGE FOR A POTENTIALLY CRIPPLING ICE STORM ACROSS PORTIONS OF CENTRAL NC. THE ARCTIC AIRMASS IN PLACE WILL RESULT IN SIGNIFICANT EVAP COOLING POTENTIAL AND THE PROGRESSIVE NATURE OF THE SHORTWAVE WILL MINIMIZE THE DURATION OF WARM ADVECTION /RETURN FLOW/ FROM THE ATLANTIC (ESP IN THE LOWEST LEVELS). ANY PRECIP THAT FALLS PRIOR TO 00Z THIS EVENING WILL BE SNOW...TRANSITIONING TO SLEET/FREEZING RAIN FROM SOUTH/SE TO NORTH/NW BETWEEN SUNSET AND MIDNIGHT AS STRONG WARM ADVECTION PUSHES A PRONOUNCED WARM NOSE INTO CENTRAL NC. THOUGH SIGNIFICANT SNOW ACCUMULATION WILL BE LIMITED TO THE FAR N/NW PIEDMONT...SIGNIFICANT ICE ACCUMULATION WILL BE POSSIBLE ELSEWHERE...WITH POTENTIALLY CRIPPLING ICE ACCUMULATION ACROSS PORTIONS OF THE TRIANGLE... COASTAL PLAIN...SANDHILLS...AND SW PIEDMONT WHERE SOME OF THE 12Z GUIDANCE IS INDICATING AS MUCH AS 0.50-1.00" OF ICE. ALTHOUGH REALITY IS LIKELY TO BE MUCH LOWER DUE TO VARIABLE PTYPES (SLEET VERSUS FZRA) AND DURATIONS...SUFFICIENT EVIDENCE IS PRESENT TO WARRANT AN INCREASE IN ICE ACCUMULATION AMOUNTS TO 0.25-0.50" SOUTH OF THE I-85 CORRIDOR...WITH THE HIGHEST AMOUNTS ALONG AND JUST SOUTH OF THE HWY 64 CORRIDOR. A SHARP GRADIENT IN ICE ACCUMULATION IS LIKELY NEAR THE SC BORDER WHERE WARM ADVECTION SHOULD ALLOW TEMPS TO RISE ABOVE FREEZING AS THE SFC LOW PROGRESSES THROUGH SC TOWARD THE NC COAST...WHICH SUPPORTS KEEPING THE SOUTHEAST COASTAL PLAIN IN A WINTER WEATHER ADVISORY. ELSEWHERE...TEMPS SHOULD STABILIZE IN THE LOWER/MID 20S ACROSS THE N/NW PIEDMONT TONIGHT AND MID/UPPER 20S ALONG THE HWY 64 CORRIDOR. IMPACT: SIGNIFICANT ICE ACCUMULATION ALONG/SOUTH OF THE HWY 64 CORRIDOR (INCLUDING TRIANGLE) WILL HAVE THE POTENTIAL TO CREATE SEVERE/PROLONGED IMPACTS ON LOCAL INFRASTRUCTURE INCLUDING DOWNED TREES/POWER LINES...POWER OUTAGES...PROPERTY DAMAGE...IMPASSABLE ROADS...ETC. -VINCENT && Link to comment Share on other sites More sharing options...
calculus1 Posted February 16, 2015 Share Posted February 16, 2015 Updated WSW for NW piedmont of NC: URGENT - WINTER WEATHER MESSAGENATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC305 PM EST MON FEB 16 2015...SIGNIFICANT WINTER STORM TO IMPACT THE WESTERN CAROLINAS ANDEXTREME NORTHEAST GEORGIA THROUGH TONIGHT....LOW PRESSURE TRACKING ACROSS THE DEEP SOUTH LATE THIS AFTERNOONWILL PASS EASTWARD THROUGH THE CAROLINAS TONIGHT. A WINTRY MIXEDBAG OF PRECIPITATION HAS ALREADY SPREAD INTO THE FORECASTAREA...AND THE INTENSITY OF THE PRECIPITATION SHOULD STEADILYINCREASE INTO THE EVENING HOURS. SNOW AND SLEET FALLING EARLY INTHE EVENT WILL GRADUALLY TRANSITION TO FREEZING RAIN FROMSOUTHWEST TO NORTHEAST...AND POSSIBLY TO ALL RAIN ACROSS SOUTHERNSECTIONS. SIGNIFICANT ACCUMULATIONS OF SNOW AND ICE AREEXPECTED...ESPECIALLY WITHIN THE WINTER STORM WARNING AREAS.NCZ035>037-056-057-502-504-506-170415-/O.CON.KGSP.WS.W.0001.000000T0000Z-150217T1200Z/ALEXANDER-IREDELL-DAVIE-CATAWBA-ROWAN-GREATER CALDWELL-GREATER BURKE-EASTERN MCDOWELL-INCLUDING THE CITIES OF...BETHLEHEM...TAYLORSVILLE...STONY POINT...STATESVILLE...MOORESVILLE...MOCKSVILLE...HICKORY...NEWTON...ST. STEPHENS...SALISBURY305 PM EST MON FEB 16 2015...WINTER STORM WARNING REMAINS IN EFFECT UNTIL 7 AM ESTTUESDAY...* LOCATIONS...THE NORTHERN FOOTHILLS AND NORTHWEST PIEDMONT OF NORTH CAROLINA.* HAZARDS...HEAVY SNOW ACCUMULATIONS ALONG AND NORTHWEST OF INTERSTATE 40...ALONG WITH SIGNIFICANT SLEET AND ICE ACCUMULATIONS MAINLY ALONG AND SOUTHEAST OF INTERSTATE 40.* TIMING...SNOW AND SLEET WILL INCREASE IN INTENSITY AND COVERAGE THROUGH THE EVENING HOURS. THE PRECIPITATION WILL BEGIN TO MIX WITH FREEZING RAIN FROM THE SOUTH THIS EVENING. THE FREEZING RAIN AND SLEET SHOULD GRADUALLY TAPER OFF OVERNIGHT...BUT WITH A POSSIBLE TRANSITION BACK TO LIGHT SNOW ACROSS THE FOOTHILLS BEFORE ENDING.* ACCUMULATIONS...SNOW AND SLEET ACCUMULATIONS OF 1 TO 3 INCHES SOUTHEAST OF INTERSTATE 40...AND 3 TO 6 INCHES NORTHWEST OF THE INTERSTATE. ABOUT ONE QUARTER OF AN INCH OF ICE IS EXPECTED...EXCEPT CLOSER TO ONE THIRD INCH IN SECTIONS SOUTHEAST OF INTERSTATE 40.* TEMPERATURES...IN THE UPPER 20S.* IMPACTS...HEAVY SNOW FALLING ON COLD ROADS...WITH SLEET AND ICE ACCUMULATIONS...WILL LIKELY CAUSE MAJOR TRAVEL PROBLEMS ALONG THE I-40 CORRIDOR LATER THIS AFTERNOON AND TONIGHT. Link to comment Share on other sites More sharing options...
griteater Posted February 16, 2015 Share Posted February 16, 2015 Haven't seen this question posed. Once sleet begins, does that indicate the warm nose has arrived (and in this case is here to stay)? Or can heavier precip rates/saturation of the column cause the precip to go back to snow? Yeah, you may be able to go over to snow with heavier rates, but yes, the warm nose is nearby and will win out in our region Link to comment Share on other sites More sharing options...
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