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January 12th-13th Cartopper Thread


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Again, go (north) west.

 

.NEAR TERM /THROUGH TONIGHT/...

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MID-UPPER LEVEL TROUGH OVER THE WRN GRT LKS WILL TAKE ON A NEGATIVE TILT AS IT MOVES EASTWARD INTO THE ERN GRT LKS AND NEW ENGLAND. STRONG H5 HEIGHT FALLS (170 METERS/12 HR) ACCOMPANYING TROUGH AXIS WILL HELP PUSH A MODIFIED ARCTIC FRONT THROUGH THE AREA AROUND 21Z AND OFF THE CHESAPEAKE BY 00Z WITH A 3-6 HR PERIOD OF CONVECTIVE PRECIP BETWEEN 18Z-00Z ACCOMPANYING FROPA. ROUGHLY EAST OF U.S. ROUTE 15 AND SOUTH OF I-70...GFS TEMP PROFILES SHOW MARGINAL LOW-LEVEL TEMPS TO SUPPORT ALL SNOW. 500-METER AND SFC WET-BULB TEMPS ARE ALL ABOVE FREEZING IN THOSE AREAS SO INCLUDED A RAIN/SNOW MIX WITH PRECIP ENDING AS A BRIEF PERIOD OF SNOW WITH NO ACCUMULATION. WEST AND NORTH OF THOSE AREAS...STEEP LAPSE RATES AND CAPE VALUES OVER 50 J/KG WILL BE CONDUCIVE TO INTENSE SNOW SQUALLS WITH WHITEOUT CONDITIONS POSSIBLE AT TIMES. A WINTER WX ADVISORY IS IN EFFECT FOR THE WESTERN FIVE ZONES WHERE UPSLOPE COMPONENT WILL ENHANCE ACCUMULATIONS. ANOTHER CONCERN IS FOR STRONG WIND GUSTS MEETING ADVISORY CRITERIA THIS EVENING. GFS INDICATES A STRONG PRES SURGE OF 6-8 MB PER 3 HRS BEHIND FROPA WITH 40-45KT IN THE LOWEST 1500 FT AVAILABLE TO MIX DOWN IN AN ENVIRONMENT CHARACTERIZED BY VERY STEEP LAPSE RATES. SREF WIND SPEED PROBS ALSO INDICATE 50-70% CHANCE OF EXCEEDING 20 MPH OVER NORTHEAST MD AND AREAS WEST OF THE BLUE RIDGE. BASED ON THESE PARAMETERS A WIND ADVISORY HAS BEEN ISSUED WITH THE STRONGEST WINDS IN THE 22Z-04Z TIME FRAME. TROUGH AXIS PUSHES EAST AFTER 00Z WITH PRECIP SHUTTING OFF QUICKLY AND INVERSION HEIGHTS LOWERING. VERY COLD WED UNDER A BRISK NW FLOW. MID-LEVEL CLOUDS WILL START MOVING IN LATE IN THE DAY AHEAD OF NEXT CLIPPER SYSTEM BUT LOW-LEVELS WILL BE TOO DRY TO SUPPORT ANY PRECIP.

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Last years squall was something I won't soon forget.  That said, I would take a small flizzard today and call it a win.  I haven't even seen flake yet, sooooooo.....I'm all in!  Why not.   :weenie:

That was awesome. I picked up close to 3" in just over an hour, with whiteout at the end. Expecting nothing like that today here. Temps too warm today ahead of the front. Probably a rain shower followed by cold and wind.

 

Places NW towards Westminster could get a nice coating I would think.

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       I think I'm a little more optimistic on this than most others, at least in terms of seeing a nice burst of snow and perhaps a whitening of grassy areas for those north of DC.     Yes, the parent NAM is uninspiring in terns of QPF and temperatures, but 12 km is not going to handle a narrow strongly-forced band.    The NAM nest and the HRRR are what we should focus on, with both showing a nice band moving through areas north of DC (and perhaps DC itself).    The 12z NAM nest and the last few HRRR runs show about 0.05 for BWI, and while the NAM nest mostly misses DCA, the 15z HRRR has 0.05 there too.     These hi-res runs also simulate strong evaporational cooling setting in quickly such that it probably does start as rain but quickly goes over to snow as temps fall into the 33-36 range.

 

        And as I've been typing this, I see that the 16z HRRR has 0.05 for DCA and 0.07 for BWI.

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