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7/27 Severe Threat Discussion and Obs


Kmlwx

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Moving the afternoon AFD from LWX into here... it discussed the threat nicely

 


AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
254 PM EDT FRI JUL 25 2014

.NEAR TERM /THROUGH SATURDAY/...
HIGH PRESSURE IS IN CONTROL TODAY AND DRY CONDITIONS WILL
PERSIST. TEMPS WILL CONTINUE TO RISE INTO THE UPPER 70S IN THE
MTNS TO THE LOW 80S NEAR THE INTERSTATE 95 CORRIDOR. HIGH PRESSURE
WILL MOVE OFF THE COAST TONIGHT AND WINDS WILL BECOME SRLY
TONIGHT. DEWPTS WILL BEGIN TO INCREASE INTO SATURDAY.

HIGH PRESSURE WILL BE WELL OFF THE EAST COAST SATURDAY MORNING AND
SRLY FLOW WILL CONTINUE TO DRAW IN HIGHER DEWPTS AS WELL AS WARMER
TEMPS. FCST MAX TEMPS WILL REACH THE MID TO UPPER 80S SATURDAY
AFTERNOON. WESTERLY FLOW ALOFT WILL LEAD TO UPSTREAM DISTURBANCES
REACHING THE MID-ATLANTIC AND A LEE TROUGH TO FORM. A SHORTWAVE
TROUGH CURRENTLY RESPONSIBLE FOR SHOWERS AND THUNDERSTORMS ACROSS
IA-IL WILL REACH THE AREA SATURDAY AFTERNOON. IT IS EXPECTED TO
WEAKEN BUT WITH THE SRLY FLOW ADVECTING WARM AND MOIST CONDITIONS
INTO THE REGION A FEW SHOWERS WILL BE POSSIBLE IN THE HIGHLANDS
AND AHEAD OF THE LEE TROUGH. AN ISOLATED THUNDERSTORM WILL BE
POSSIBLE ACROSS THE I-95 CORRIDOR SAT AFTERNOON. ACTIVITY WILL
WANE TOWARDS SUNSET.

A STRONG SHORTWAVE TROUGH WILL DROP INTO THE NRN PLAINS SATURDAY
WHILE CONVECTION WILL BE ONGOING AHEAD OF A COLD FRONT ACROSS THE
MIDWEST SATURDAY AFTERNOON AND EVENING. SOME SHOWERS AND
THUNDERSTORMS ARE EXPECTED TO BECOME SEVERE AND THIS ACTIVITY WILL PROPAGATE
EASTWARD AND POTENTIALLY IMPACT THE POTOMAC HIGHLANDS LATE
SATURDAY NIGHT/EARLY SUNDAY MORNING. THERE ARE UNCERTAINTIES
PERTAINING TO THE TRACK OF A POTENTIAL MCS SUNDAY MORNING WHICH
WILL THEN IMPACT THE AMT OF CLOUD COVER AND THEREFORE INSTABILITY
THE MID- ATLANTIC GAINS ON SUNDAY.



&&

.SHORT TERM /SATURDAY NIGHT THROUGH SUNDAY/...
A WARM FRONT WILL MOVE ACROSS THE REGION SATURDAY NIGHT/SUN
MORNING AND MOISTURE WILL CONTINUE TO ADVECT INTO THE MID-ATLANTIC
SUNDAY. LOW PRESSURE WILL BE ACROSS THE GREAT LAKES AND A COLD
FRONT WILL BE STRETCHED FROM PA TO OHIO TO MO. AS THE STRONG
SHORTWAVE TROUGH NEARS SHEAR WILL INCREASE AND SHOWERS AND
THUNDERSTORMS ARE LIKELY. DEPENDING ON THE AMT OF INSTABILITY THE
REGION GETS WITH THE DEPARTING MCS FROM THE OHIO VALLEY... SEVERE
STORMS MAY BE POSSIBLE WITH THE THREATS OF DMG WINDS LARGE HAIL
ISOLATED TORNADOES AND HEAVY RAIN. SREF ENSEMBLE MEMBERS SHOW A
RANGE OF CAPE SOLUTIONS FOR SUNDAY WITH 500 TO 3000 J/KG POSSIBLE.
ONE THING THAT IS CERTAIN IS THAT SHEAR PROFILES INCREASE SUNDAY
AND HODOGRAPHS BECOME LINEAR WITH 40-50 KTS AT 10-15K FEET. A
STRONG LINE OF THUNDERSTORMS WILL BE POSSIBLE SUN AFTERNOON AND
EVENING.


OUTFLOW BOUNDARIES AND THE CLOSE PROXIMITY TO THE SFC LOW ACROSS
OH/PA/NY WILL LEAD TO THE THREAT OF SVR THUNDERSTORMS CAPABLE OF
PRODUCING TORNADOES.
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Sorry, a off topic question. I was on fort Foote road, in Fort Washington today (next to national harbor). I noticed a LOT of tree damage in a small area. Looks like about a month old. Down burst?

About a month, or 5 or 6 weeks ago, a storm system came through Belle Haven in Va. and crossed over the river in MD. This storm caused major damage in Belle Haven and then in the Ft. Washington area of PG county. A powerful downburst created a lot of havoc in the area. I personally spent 10 afternoons with a chainsaw clearing debris.

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The most recent SREF run on SPC site is less impressive. Crossing my fingers for actual interesting weather. It will probably fail...

 

Areas further west into WV and the mid/upper OH Valley are definitely a better play on Sunday than the MA.

 

The NAM's track record this Spring/Summer has been enough to toss it most times.

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30% hatched D2 with a mod risk to the west, full spectrum of severe hazards mentioned with the convective signal across the suite being highlighted.

 

Sunday could be quite an impressive day with multiple areas of enhanced potential. An anomalous setup with a powerful upper trough like this in July certainly has the potential to be a showstopper.

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DAY 2 CONVECTIVE OUTLOOK AMEND 1

NWS STORM PREDICTION CENTER NORMAN OK

0106 AM CDT SAT JUL 26 2014

VALID 271200Z - 281200Z

...THERE IS A MDT RISK OF SVR TSTMS ACROSS MUCH OF ERN KY...SRN

OH...AND WV...

...THERE IS A SLGT RISK OF SVR TSTMS FROM THE OH/TN VALLEYS EWD

ACROSS THE MID ATLANTIC AND NEW ENGLAND STATES...

AMENDED FOR SIG GRAPHIC

...SUMMARY...

TORNADOES...DAMAGING WINDS AND LARGE HAIL ARE EXPECTED ACROSS MUCH

OF EASTERN KENTUCKY...SOUTHERN OHIO AND WEST VIRGINIA DURING THE

AFTERNOON AND EVENING. SEVERE WEATHER IS ALSO EXPECTED ACROSS MUCH

OF THE MID-ATLANTIC AND NORTHEASTERN STATES WITH MAINLY DAMAGING

WINDS AND HAIL. ISOLATED HAIL AND WIND IS ALSO POSSIBLE ACROSS

SOUTHEASTERN ARIZONA.

...SYNOPSIS...

AN IMPRESSIVE UPPER TROUGH WILL DIVE SEWD FROM THE UPPER MS VALLEY

INTO THE OH VALLEY ON SUNDAY WITH MID TO UPPER LEVEL WINDS

INCREASING TO 60-90 KT RESPECTIVELY. AT THE SURFACE...THE PRIMARY

SURFACE LOW WILL TAKE SHAPE FROM LOWER MI INTO OH DURING THE

DAY...WITH SURFACE TROUGH/FRONT FROM OH SWWD ALONG THE OH RIVER.

PRECEDING THE COLD FRONT WILL BE CLUSTERS OF STORMS...PERHAPS A

SEVERE MCS...OVER SRN OH/WV/ERN KY IN THE MORNING...AND THIS MAY

AFFECT VA LATER IN THE DAY. OUTFLOW FROM THIS POTENTIAL MCS MAY AID

TORNADO POTENTIAL ACROSS THE MDT RISK AREA LATER IN THE DAY WHEN

WSWLY SURFACE WINDS AND COOLING ALOFT STRONGLY DESTABILIZE THE AREA.

TO THE E...A SURFACE TROUGH WILL ALSO DEEPEN E OF THE APPALACHIANS

WITH S WINDS BRINGING ATLANTIC MOISTURE NWD ACROSS THE DELMARVA AS

WELL AS INTO SRN NEW ENGLAND DURING THE DAY. AN UPPER-LEVEL

DISTURBANCE MAY AID IN RELATIVELY EARLY SEVERE STORM DEVELOPMENT

FROM ERN NY INTO SRN NEW ENGLAND WITH A SECOND ROUND OF STORMS

OCCURRING OVERNIGHT.

MOISTURE AND LIFT WITH A WWD-MOVING DISTURBANCE ACROSS NRN

MEXICO/SRN AZ MAY RESULT IN ISOLATED HAIL OR WIND.

...ERN INDIANA...CNTRL AND ERN KY...OH...WV...

A MORNING MCS IS LIKELY TO TRAVERSE THIS AREA AND MOST LIKELY AFFECT

THE SRN OH/ERN KY/WV AREA IN THE MORNING WITH AN ONGOING WIND

THREAT. BEHIND THIS SYSTEM...THE VEERED NATURE OF THE LOW-LEVEL FLOW

SHOULD ALLOW FOR RAPID DESTABILIZATION WITH UPPER 60S/LOWER 70S F

DEWPOINTS AS WELL AS EVENTUAL COOLING ALOFT WITH THE UPPER TROUGH.

AS FORCING FOR ASCENT INCREASES DURING THE AFTERNOON...STORMS SHOULD

FORM ALONG THE FRONT OVER ERN IND...WRN OH...AND INTO NRN

KY...MATURING AS THEY MOVE ESEWD INTO ERN KY...SRN OH...AND AGAIN

WV. STEEP LAPSE RATES ALOFT AND LONG HODOGRAPHS WILL SUPPORT ROBUST

SUPERCELLS WITH VERY LARGE HAIL LIKELY. RELATIVELY LOW LCLS AND

ENHANCED SRH MAY ALSO SUPPORT AN APPRECIABLE TORNADO THREAT. A

STRONG TORNADO OR TWO MAY OCCUR...ALTHOUGH THE PRECISE AREA WILL NOT

BE KNOWN UNTIL THE MORNING ACTIVITY DEPARTS AND MESOSCALE BOUNDARIES

SETUP.

...WV INTO PA AND NJ LATE...

A SEVERE MCS IS FORECAST TO EVOLVE OUT OF THE MDT RISK AREA...WITH

DAMAGING WINDS AND HAIL POSSIBLE ALONG THE LOW TRACK...AIDED BY A

STRONG VORT MAX AND ENHANCED CONVERGENCE WITH THE SURFACE LOW. A

TORNADO CANNOT BE RULED OUT WITH THIS ACTIVITY DUE TO BETTER

LOW-LEVEL SHEAR NEAR THE LOW.

...NRN VA...MD...DE...PA...NJ LATE AFTERNOON THROUGH EVENING...

AN MCS IS LIKELY TO BE ONGOING SOMEWHERE NEAR WV SUN MORNING...AND

IT IS UNCLEAR WHETHER IT WILL PERSIST INTO VA AND MD DURING THE DAY.

EVEN IF IT DOES NOT REMAIN INTACT...OUTFLOW BOUNDARIES...AS WELL AS

INCREASING CONVERGENCE WITH THE LEE SURFACE TROUGH SHOULD PROVIDE

ADDITIONAL FOCUS FOR SEVERE STORMS BY LATE AFTERNOON. SHEAR PROFILES

WILL BECOME QUITE FAVORABLE FOR SUPERCELLS WITH TIME...AND PLENTY OF

INSTABILITY WILL BE PRESENT TO SUPPORT THEM. LARGE HAIL WILL BE

LIKELY...AND A COUPLE TORNADOES WILL ALSO BE POSSIBLE GIVEN CELLULAR

STORM MODE AND MODESTLY-LOOPING HODOGRAPHS. THERE IS A STRONG

CONVECTIVE SIGNAL IN SEVERAL MODELS ACROSS MD...ERN VA AND DE NEAR

00Z.

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Wow...not often you see that kind of early day 2 outlook around these parts. Interesting shape to the hatching - 6z NAM looks like it backed off a little bit from last night. Also SREF and NAM continue to focus best parameters just to the south of the DC area. 

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When Midwest/central people show up in a MA thread, it's time to pay attention

Ellinwood thinks SPC was a bit on the bullish side given the uncertainty. 6z NAM for us was definitely not like the 0z NAM. He thinks 30% somewhere east of the apps will be needed but still a lot to be worked out. We'll need to see more runs like the NAM of last night if we want to hold higher potential. 

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From the 3 am AFD from LWX...

 

LONG TERM /SUNDAY THROUGH FRIDAY/...

THE PRIMARY ACTION DURG THE XTND PD LOOKS TO BE COMING AT THE
BEGINNING. SYNOPTICALLY THIS SUMMER CERTAINLY HAS BEEN OUT OF THE
NORM (IE..AN ABSENCE OF THE SUB TROP HIGH) AND IT LOOKS LK THIS WL
HOLD TRUE FOR THE END OF JUL AS WELL.

IT APPEARS THAT AN UNUSUALLY STRONG AREA OF LOW PRES WL BE
TRACKING ACROSS PA SUN EVE. THIS WL PLACE THE MID ATLC SUN IN AN
UNSTABLE AIR MASS W/ CAPES OVR 1000. SPC HAS ENTIRE CWA IN A SLT
RISK. ONE THING THAT WOULD MAKE THIS THREAT STRONGER IS IF AREA GETS
BRKS IN CLDS DURG MIDDAY TO ALLOW FOR HTG/INSTABILITY. HIGHS SEASONABLE...
GNRLY IN U80S...PSBLY 90 IN THE CIITES.

CHC FOR RA/TSTMS XPCTD TO CONT SUN NGT AHD OF A CD FNT. HOW MUCH
INSTABILITY WL RMN POST-SUNSET WL HELP TO DETERMINE IF THERE WL BE
A CONT SVR THREAT. LOWS RANGING FM THE M60S TO L70S.

CURRENTLY IF LOOKS LK THE ACTUAL CD FNT WON`T PUSH E OF THE RGN
UNTIL LATE MON...HENCE MORE POPS/CHCS FOR CNVCTN. HIGHS IN LM80S.

 

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