Apr 21-23 MidAtl/NE Storm, Reality: Short Range [0-4 days] Options

[Superstorm93]

Futurecast

4-5" for NNJ

[NYCSuburbs]

That's the point I made. There are two obvious extremes when it comes to Flash Flooding.

1. Oversaturated ground doesn't allow for water to be soaked in leading to Flash Flooding.
2. Drought stricken ground acts like a sponge that's been dry for too long and immediately gets overwelmed.

The second extreme will come into play here... over the last few weeks the ground was so dry in some areas that dirt almost felt like solid rock when walking on it. There's also supposed to be a few hours late tomorrow evening/early night when much heavier rain rates move through, making this more of a flash flood as opposed to a prolonged steady light-moderate rain.

[NYCSuburbs]

Futurecast

4-5" for NNJ

Can you post the FutureCast link? I lost the old one I had somehow and can't find it.

[Superstorm93]

Can you post the FutureCast link? I lost the old one I had somehow and can't find it.

Sure

They have a pretty decent new website now

[sw03181]

LOL just when I thought winter was done...

Wonder if there will be snow mixing in during the Pirates game on Monday night.

[NYCSuburbs]

Sure

They have a pretty decent new website now

Thanks, their website actually looks really nice....

[grandpaboy]

Though the outcome will be different(as far as areas effected by snow)....one can't ignore the oblivious .....two extreme mid latitude deep LP's bringing out season conditions in an otherwise non seasonal fall,winter, and spring to the MA/NE......pretty crazy stuff....

[NorEaster07]

Started an OBS thread since I'm calling it a night. Moisture will be entering mid atlantic overnight. Should be fun tracking everything tomorrow.

[jdrenken]

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PITTSBURGH PA
821 PM EDT SAT APR 21 2012

.SYNOPSIS...
COLDER AND DRIER AIR WILL MOVE INTO THE REGION OVERNIGHT. A STORM SYSTEM
WILL MOVE NORTH TOWARD THE REGION LATER SUNDAY WITH RAIN THAT WILL
CHANGE TO SNOW AND INCREASE IN INTENSITY THROUGH MONDAY MORNING.
TEMPERATURES WILL MODERATE BY MID-WEEK.

&&

.NEAR TERM /UNTIL 6 AM SUNDAY MORNING/...
ONLY A BIT OF DRIZZLE LEFT ACROSS THE SOUTHEAST RIDGES OTHERWISE
CHILLY WITH CLOUDS REMAINING OVERNIGHT. NORTHERLY LOW LEVEL FLOW
WILL CONTINUE TO ADVECT SIGNIFICANTLY COLDER AIR INTO THE CWA.
TEMPERATURES AT 850 MB WILL FALL TO ABOUT -2C AT KPIT BY MORNING.
WITH CLOUDS HOLDING IN OVERNIGHT SHOULD NOT BE A FREEZE OR FROST.

&&

.SHORT TERM /6 AM SUNDAY MORNING THROUGH MONDAY NIGHT/...
WHILE SIGNIFICANT COLD AIR ADVECTION WILL BE CONTINUING IN THE
LOW LEVELS THROUGH SUNDAY EVENING...THE REAL COLD KICK STARTS UP
OVERNIGHT SUNDAY NIGHT. CONSENSUS 850 MB TEMPERATURES CRATER TO -5
TO -6C ON THE NAM/GFS/ECMWF/GEM AT THE SAME TIME A STRONGLY
COUPLED AND FAVORABLY CURVED DIVERGENT UPPER JET STREAK PATTERN
STREAKS NORTHWARD TOWARD WESTERN PENNSYLVANIA. AT THE SAME
TIME...THE 850 MB LOW TRACKS GENERALLY TO THE EAST OF THE
CWA...YIELDING NORTH-NORTHEASTERLY FLOW AT 850 MB TOPPING 65 KTS
PER THE NAM AND WELL IN EXCESS OF 50 KTS PER THE GFS. THE NOSE OF
THIS LOW-LEVEL JET- IKE FLOW POINTS SQUARELY AT THE PITTSBURGH
METRO AREA PER THE NAM...AND JUST TO THE EAST PER THE GFS. THE
COMBINATION OF THOSE TWO FACTORS YIELDS AN IMPRESSIVE SWATH OF
NEGATIVE OMEGAS PER BOTH MODELS ACROSS WESTERN PENNSYLVANIA FOR IN
EXCESS OF 18 HOURS FROM SUNDAY NIGHT THROUGH MONDAY...ENOUGH THAT
DYNAMICAL COOLING SEEMS ALL BUT A FOREGONE CONCLUSION. BUFKIT
SOUNDINGS SUPPORT THIS CONCLUSION AND YIELD ALMOST NO DIURNAL
TEMPERATURE RISES ON MONDAY AFTER TEMPERATURES FALL NEAR FREEZING
SUNDAY NIGHT. ALL IN ALL...IT WOULD SEEM THAT IN THE AREA OF THE
STRONGEST OMEGAS...SNOW WILL BE THE DOMINANT PRECIPITATION TYPE
THROUGHOUT THE EVENT.

WHILE THE SYNOPTIC SETUP IS RATHER IMPRESSIVE...THE SMALLER SCALE
NUTS AND BOLTS GIVE A SOMEWHAT BLURRIER PICTURE. ICE MICROPHYSICS
DO NOT REALLY SUPPORT A PARTICULARLY HIGH RATIO EVENT. THE
DENDRITIC GROWTH LAYER OF -12 TO -20C IS BARELY SATURATED...AND
THROUGHOUT THE TIME OF THE STRONGEST ASCENT...THE NEGATIVE OMEGA
BULLS EYE IS GENERALLY LOCATED BELOW THE -12 TO -20C LAYER.
COMBINING THIS WITH A BOUNDARY LAYER PROFILE THAT IS RATHER
MARGINAL AND GENERALLY WITHIN 1C OF FREEZING FOR ALMOST THE ENTIRE
DEPTH OF THE MIXED LAYER MAKES FOR A FAIRLY TENUOUS SNOWFALL
FORECAST. HOWEVER...FAIRLY DECENT FLOW DEFORMATION IN THE 850-700
MB LAYER COUPLED WITH STRONG FRONTOGENETICAL FORCING AS WELL AS
SOME EPV REDUCTION IN THE UPWARD BRANCH OF THE FRONTOGENETICAL
CIRCULATION ON THE TROWAL PERIPHERY YIELDS VERY HIGH CONFIDENCE IN
QPF VALUES IN EXCESS...AND POSSIBLY WELL IN EXCESS...OF 0.4
INCHES IN THE AREA OF STRONGEST LIFT. AS A RESULT...EVEN WITH
UNIMPRESSIVE RATIOS AND A MARGINAL BOUNDARY LAYER...PRECIPITATION
RATES SHOULD BE IMPRESSIVE ENOUGH TO ALLOW SNOW TO PILE UP. EVEN
USING RATIOS OF 7-8:1 IN THE RIDGES...4-5:1 AROUND PITTSBURGH...AND
MUCH LOWER THAN THAT IN POINTS TO THE SOUTH AND WEST...AT LEAST
SOME SNOW ACCUMULATION IS LIKELY ON A WIDESPREAD BASIS. IN
FACT...HEAVY SNOW ACCUMULATION IS POSSIBLE GENERALLY IN THE RIDGES
AND FROM PITTSBURGH NORTHEASTWARD WHERE THE CONFLUENCE OF
LIFT...COLDER AIR...AND A LONGER DURATION WILL MAKE RATIOS A BIT
HIGHER. ALL IN ALL...QPF WILL DRIVE THE HIGH SNOW
ACCUMULATIONS...RATHER THAN THE RATIOS. STORM TOTAL QPF VALUES IN
THE AFOREMENTIONED SETUP STRADDLE 2 INCHES IN THE AREAS OF BEST
LIFT...WHICH EVEN WITH THE UNIMPRESSIVE RATIOS STILL RESULT IN 6
OR MORE INCHES OF SNOW. AS A RESULT...WINTER STORM WATCHES WERE
POSTED FOR THE RIDGES AND ALL AREAS NORTH AND EAST OF PITTSBURGH.
FUTURE SHIFTS WILL LIKELY NEED TO REFINE THE BEST SNOW/QPF
AXIS...HOWEVER THE MODEL CONSENSUS WAS STRONG ENOUGH FOR THE PAST
THREE CYCLES SUCH THAT CONFIDENCE HAS GROWN TO GREATER THAN 50
PERCENT THAT A SIGNIFICANT SNOWFALL IS POSSIBLE DURING THE SUNDAY
NIGHT INTO MONDAY NIGHT TIME FRAME. FRIES

[jdrenken]

Please post in OBS thread.