Flash Flooding and Flood in Maryland, April 22, 2006

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
1020 PM EDT FRI APR 21 2006

.EVENING UPDATE...

HAVE BACKED OFF TO SCTD SHWRS TIL 3 AM...THEN HAVE ADTNL ACTIVITY
EXPECTED TO REDEVELOP THROUGH DAYBREAK ACROSS THE CWA WITH 100 POPS
AS S/W TROUGH APPROACHES AND STRONG MOISTURE ADVECTION CONTINUES.
HAVE CONTINUED TO MENTION ISO TSTM LATE TNGT ACROSS THE SOUTHERN CWA
WHERE INSTABILITY REMAINS A BIT BETTER ALONG WITH BETTER FORCING.
SCA CONDS OCCURRING ACROSS MOST OF THE WATERS ATTM AND SEE NO REASON
TO BACK OFF THE SCA WE ALREADY HAVE IN PLACE.

SLGT RISK CONTINUES FOR SATURDAY ACROSS A LARGE CHUNK OF THE SRN
CWA. THIS STILL LOOKS DECENT...BUT DEPENDS ON HOW STRONG THE
SATURATED MARINE LYR PROVES TO BE TO THE SOUTH. AT ANY RATE...IT
STILL LOOKS LIKE A THREAT WORTH WATCHING. ALSO WORTH KEEPING AN EYE
ON IS OUR THREAT FOR MINOR CSTL FLDG ALONG THE WESTERN SHORE OF THE
BAY AND IN THE TIDAL POTOMAC.

JB

&&

.SHORT TERM /TONIGHT THROUGH SATURDAY/...
VERY TOUGH FORECAST TODAY FOR THE NEXT 24H. WMFNT DRAPED ACROSS THE
CWA ATTM SEPARATES A COOL MARITIME FLOW DAMMED UP AGAINST THE MTNS
ACROSS THE NORTHERN HALF OF THE CWA. DECENT LOW LEVEL JET DEVELOPS
TONIGHT WITH SOME MODEST ELEVATED INSTABILITY AND GOOD FORCING AS
STRONG SHORTWAVE APCHS FROM THE SOUTHWEST. GOOD FORCING OVERALL
THROUGH TOMORROW AND UPR DIVERGENCE ISN/T BAD EITHER. GOOD MOISTURE
PLUME CONTINUES TO ADVECT INTO THE AREA. HEAVY RAINFALL LOOKS TO BE
A GOOD BET BOTH TONIGHT AND AGAIN TOMORROW AS THE WEAK FRONT
APPROACHES FROM THE WEST. ASIDE FROM ANY LOCALIZED POOR DRAINAGE
PROBLEMS TONIGHT...GIVEN ANTECEDENT SOIL CONDITIONS FLOODING
PROBABILITY LOOKS TO BE LOW. HEAVY RAINFALL WITH THE FRONT TOMORROW
WILL HAVE TO BE WATCHED DEPENDING ON HOW MUCH RAINFALL OCCURS
TONIGHT. OVERALL CONFIDENCE IN POTENTIAL FLOODING TOMORROW TOO LOW
FOR A WATCH AT THIS POINT.

SOME POTENTIAL FOR SVR OVER THE FAR SOUTHEAST TOMORROW PROVIDED THAT
SOME INSTABILITY IS ABLE TO DEVELOP. RIGHT NOW LOOKS LIKE THE
EXTENSIVE CLOUD COVER WILL BE TOO MUCH TO ALLOW ANY APPRECIABLE
INSOLATION. WIND FIELD IS DEFINITELY GOOD TOMORROW ON THE RETREATING
WARM FRONT. WILL CONTINUE TO MENTION IN HWO FOR NOW.

&&

.LONG TERM /SATURDAY NIGHT THROUGH FRIDAY/...
THE WEATHER WILL REMAIN UNSETTLED THROUGH THE FIRST HALF OF NEXT
WEEK. HIGH PRESSURE IS EXPECTED TO BUILD BACK OVER THE REGION BY
LATE WEDNESDAY AND CONTINUE THROUGH FRIDAY.

THE FIRST PART OF THE EXTENDED WILL DEAL WITH AN EXITING LOW
PRESSURE SYSTEM AND ASSOCIATED FRONTAL BOUNDARY. THE PRECIP LOOKS TO
GRADUALLY TAPER OFF BETWEEN 00Z AND 06Z IN MOST LOCALES WITHIN THE
CWFA. COLD FRONT WILL CONTINUE SOUTHWARD OVERNIGHT AND STALL OVER
CENTRAL NORTH CAROLINA BY MONDAY. HIGH PRESSURE BRIEFLY IN PLACE AT
THE SURFACE ON MONDAY...BUT THE NEXT SYSTEM IS EXPECTED ON TUESDAY.
STALLED BOUNDARY OVER NORTH CAROLINA WILL BEGIN MOVING NORTH LATE
MONDAY/EARLY TUESDAY IN ADVANCE OF A COLD FRONT. THE FRONT IS
EXPECTED TO MOVE THROUGH BY LATE TUESDAY. BY EARLY WEDNESDAY THE
FRONT IS EXPECTED TO BE ALONG THE VA/NC BORDER AS HIGH PRESSURE
BUILDS BACK IN OVER THE CWFA. HIGH PRESSURE WILL REMAIN IN PLACE
THROUGH THE REMAINDER OF THE WEEK.

MOS GUIDANCE WAS PRETTY CLUSTERED WITH POPS AND TEMPS. SPLIT THE
DIFFERENCE.

&&

.AVIATION...
PROLONGED LOW CIG IFR EVENT APPEARS LIKELY TONIGHT AND TOMORROW.
COLD AIR DAMMING HAS WEDGED IN AS FAR SOUTH AS KEZF AS OF EARLY THIS
AFTN. MODERATE LLJ WILL DEVELOP OVER THE SURFACE COLD POOL WHICH
WILL LEAD TO LLWS PROBS OVERNIGHT AS LLJ DEVELOPS. ELEVATED
CONVECTION ALSO APPEARS LIKELY TONIGHT ADDING TO THE CHALLENGES
TONIGHT AVIATION WISE. PRIMARY PROB OVERNIGHT APPEARS TO BE LOW CIGS
AS SURFACE WINDS WILL STAY UP AND PRECIPITATION WILL BE OCCURRING
WHICH SHOULD KEEP VSBYS FROM CRASHING TOO FAR. CIGS ON THE OTHER
HAND WILL BE APPROACHING LIFR BEGINNING LATE THIS EVENING AT THE
METRO ARPTS.

HOW LOW WILL THE CIGS GET REMAINS PROBLEMATIC AT THIS POINT. MUCH
GUIDANCE POINTS TO CIGS APPROACHING ILS CAT 1 MINS AND STAYING THAT
WAY FOR MANY HOURS. WHILE PROLONGED LOW CIG/VIS EVENTS ARE FAVORED
WITH COLD AIR DAMMING SITUATIONS WIND DIRECTION OVERNIGHT LOOKS TO
BE JUST SOUTH OF EAST AND THE GROUND IS WARM. RIGHT NOW HAVE GOOD
CONFIDENCE IN CIGS IN THE 400-600 FT RANGE OVERNIGHT...BUT LESS
CONFIDENT OF CIGS DIPPING MUCH BELOW THAT FOR ANY EXTENDED PERIODS.

&&

.MARINE...
HAVE EXTENDED THE SMALL CRAFT ADVISORY OUT THROUGH MOST OF
SATURDAY. BELIEVE WINDS A TAD BIT LOW WITHIN THE MODELS.

WILL HAVE TO MONITOR THE WATER LEVELS ON THE WESTERN SHORE OF THE
CHESAPEAKE WITH THE PROLONGED EASTERLY FLOW. TIDAL FLOODING MAY
BE POSSIBLE DURING THE TIME OF HIGH TIDE TOMORROW...AROUND MIDDAY.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...NONE.
MD...NONE.
VA...NONE.
WV...NONE.
MARINE...SMALL CRAFT ADVISORY FOR ANZ530>537 UNTIL 11 PM SATURDAY.
&&

SHORT TERM...MANNING
LONG TERM...LISTEMAA
AVIATION...

MARINE...

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
1014 AM EDT SAT APR 22 2006

ANZ530>537-DCZ001-MDZ002>007-009>011-013-014-016>018-VAZ021-
025>031-036>042-050>057-WVZ048>055-231000-
CHESAPEAKE BAY NORTH OF POOLES ISLAND MD-
CHESAPEAKE BAY FROM POOLES ISLAND TO SANDY POINT MD-
CHESAPEAKE BAY FROM SANDY POINT TO NORTH BEACH MD-
CHESAPEAKE BAY FROM NORTH BEACH TO DRUM POINT MD-
CHESAPEAKE BAY FROM DRUM POINT MD TO SMITH POINT VA-
TIDAL POTOMAC FROM KEY BRIDGE TO INDIAN HEAD MD-
TIDAL POTOMAC FROM INDIAN HEAD TO COBB ISLAND MD-
TIDAL POTOMAC FROM COBB ISLAND MD TO SMITH POINT VA-
DISTRICT OF COLUMBIA-ALLEGANY-WASHINGTON-FREDERICK MD-CARROLL-
NORTHERN BALTIMORE-HARFORD-MONTGOMERY-HOWARD-SOUTHERN BALTIMORE-
PRINCE GEORGES-ANNE ARUNDEL-CHARLES-ST. MARYS-CALVERT-HIGHLAND-
AUGUSTA-ROCKINGHAM-SHENANDOAH-FREDERICK VA-PAGE-WARREN-CLARKE-
NELSON-ALBEMARLE-GREENE-MADISON-RAPPAHANNOCK-FAUQUIER-LOUDOUN-
ORANGE-CULPEPER-PRINCE WILLIAM/MANASSAS/MANASSAS PARK-FAIRFAX-
ARLINGTON/FALLS CHURCH/ALEXANDRIA-STAFFORD-SPOTSYLVANIA-
KING GEORGE-GRANT-MINERAL-HAMPSHIRE-MORGAN-BERKELEY-JEFFERSON-
PENDLETON-HARDY-
1014 AM EDT SAT APR 22 2006

THIS HAZARDOUS WEATHER OUTLOOK IS FOR MARYLAND WEST OF THE
EASTERN SHORE INCLUDING THE CHESAPEAKE BAY AND EAST OF GARRETT
COUNTY...EASTERN WEST VIRGINIA...NORTHERN AND CENTRAL VIRGINIA...
WASHINGTON DC AND THE TIDAL POTOMAC RIVER.

.DAY ONE...TODAY AND TONIGHT

A SMALL CRAFT ADVISORY IS IN EFFECT FOR THE TIDAL POTOMAC RIVER AND
MARYLAND PORTION OF THE CHESAPEAKE BAY THROUGH EARLY THIS EVENING.

RAINFALL THROUGH TONIGHT COULD REACH 3 INCHES IN A FEW ISOLATED
SPOTS. THIS COULD BE SUFFICIENT TO GENERATE AREAS OF DEEP STANDING
WATER...BUT SIGNIFICANT FLOODING IS NOT ANTICIPATED DUE TO DRIER
THAN NORMAL CONDITIONS RECENTLY.

SOUTHEASTERLY WINDS TODAY WILL CAUSE TIDES ON THE CHESAPEAKE
BAY...TIDAL POTOMAC AND OTHER ESTUARIES TO BE ABOVE NORMAL. LEVELS
COULD BE UP TO ONE FOOT ABOVE NORMAL BY DAYS END...CREATING MINOR
OVERFLOWS AT TIME OF HIGH TIDE IN VERY LOW LYING PORTIONS OF
ANNAPOLIS AND ALEXANDRIA.

.DAYS TWO THROUGH SEVEN...SUNDAY THROUGH FRIDAY

HAZARDOUS WEATHER IS NOT EXPECTED.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION IS NOT ANTICIPATED.

ROGOWSKI