Flash Flood Warning 10, NWS Albany, NY

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ALBANY NY
140 AM EDT WED AUG 6 2003

.DISCUSSION...
THE MAIN PROBLEM OF THE DAY REGARDS WHETHER TO ISSUE A FLOOD WATCH
FOR THE ALBANY COUNTY WARNING AREA FOR TODAY.  THERE WAS SOME
FLOODING YESTERDAY, BUT AREALLY, IT WAS FAR SHORT OF THE 30 PERCENT
COVERAGE FOR WHICH A FLOOD WATCH WOULD BE REQUIRED.  FOR TODAY, LIKE
YESTERDAY, IT IS ALL BUT IMPOSSIBLE TO TELL WHERE HEAVY
PRECIPITATION WILL OCCUR (JUST LOOK AT MODEL GUIDANCE).  BUT IT
CERTAINLY IS A POSSIBILITY, EVEN THOUGH THE TOTAL PRECIPITABLE WATER
IS FORECAST TO BE ONLY A BIT OVER AN INCH, WHEREAS YESTERDAY IT WAS
JUST SHY OF AN INCH AND THREE QUARTERS.  IT SEEMS BEST NOT TO ISSUE
A BLANKET COUNTY WARNING AREA FLOOD WATCH FOR TODAY.  THE BEST
APPROACH SEEMS TO BE TO OBSERVE IF, AND WHERE, ANY THREATENING
RAINFALL DEVELOPS AND ISSUED FLOOD WATCH TARGETED FOR THOSE SPECIFIC
AREAS.

THERE WAS A COMPLEX OF HEAVY SHOWERS AND THUNDERSTORMS OVER EASTERN
PENNSYLVANIA WHICH APPEARED LIKELY TO MOVE INTO SOUTHEASTERN NEW
YORK LATER THIS MORNING.  ANOTHER AREA OF HEAVY PRECIPITATION
OCCURRED IN NORTHERN NEW YORK BEFORE MIDNIGHT.  THIS WAS LOOPING
WESTWARD NORTH OF LAKE ONTARIO JUST AFTER MIDNIGHT.

THE MAIN PLAYER IN YESTERDAYS PRECIPITATION ENHANCEMENT WAS SOME
WAVE ACTION INDUCED BY THE TROUGH TO THE WEST, WHICH FINALLY SHOWED
SOME GOOD EASTWARD PROGRESSION AND EVOLVED, PARTIALLY AT LEAST, INTO
A RATHER STRONG-SHORT WAVE TROUGH.  THIS SHORT-WAVE MOVING THROUGH
THE LARGER-SCALE TROUGH ORIENTED IT INTO A SLIGHTLY NEGATIVE TILT.
A WIND MAXIMUM OF NEAR 100 KNOTS MOVED OVER CENTRAL NEW YORK TUESDAY
EVENING, AND THIS FEATURE WAS ASSOCIATED WITH ENOUGH DYNAMICS TO
ENHANCE THE PRECIPITATION, ESPECIALLY IN THE NORTHERN AND WESTERN
PORTION OF THE COUNTY WARNING AREA.  THE UPPER-LEVEL TROUGH COULD BE
OBSERVED WELL IN THE WATER VAPOR IMAGERY AROUND THE MIDNIGHT.  THERE
WERE 2 CENTERS OF HIGH-LEVEL VORTICITY EVIDENT IN THE ANIMATION.
ONCE WAS IN THE VICINITY OF WESTERN PENNSYLVANIA, WHILE A SECOND WAS
NEAR THE SOUTH SHORE OF JAMES BAY.  THE MODELS INITIALIZED WITH
HEIGHT NADIRS IN EACH LOCATION.  THE VORTICITY MAXIMUM IN
PENNSYLVANIA IS FORECAST TO MOVE INTO, AND THROUGH THE COUNTY
WARNING AREA TODAY AS THE UPPER-LEVEL LOW MOVES ACROSS THE REGION
AND INTO NEW ENGLAND TONIGHT.  THE WIND MAXIMUM ON THE EAST SIDE OF
THIS APPROACHING SHORT-WAVE TROUGH WAS FORECAST TO MOVE INTO NEW
ENGLAND LATER TODAY.  THE ORIENTATION AND MOVEMENT OF THIS WIND
MAXIMUM WOULD SUPPORT THE BEST HIGH-LEVEL DIVERGENCE OVER NORTHERN
NEW YORK AND NORTHERN NEW ENGLAND NORTHWARD INTO SOUTHERN ONTARIO
AND QUEBEC PROVINCES.  THE AIR IS FORECAST TO BE ABOUT EQUALLY
CONDITIONALLY UNSTABLE ACROSS THE ENTIRE REGION TODAY.  THE ETA
MODEL FORECASTS THE BEST LOW-LEVEL CONVERGENCE TO BE ACROSS NORTHERN
NEW YORK AND NORTHERN NEW ENGLAND TODAY, WHILE THE NESTED GRID MODEL
FORECAST IT FURTHER SOUTH IN THE COUNTY WARNING AREA.

THE MODEL PRECIPITATION FORECASTS VARIED CONSIDERABLY.  THE ETA
FORECAST THE HEAVY PRECIPITATION NORTH OF NEW YORK AND NEW ENGLAND
TODAY, CONSISTENT WITH THE AFOREMENTIONED DYNAMIC SIGNATURES.  THE
NESTED GRID FORECAST HAD HEAVY PRECIPITATION NORTH TOO, BUT HAD A
SECOND AREA, WITH A MODERATE AMOUNT OF RAINFALL ACROSS MUCH OF THE
COUNTY WARNING AREA.  THE AVIATION MODEL FORECAST THE HEAVIEST
PRECIPITATION IN SOUTHEASTERN NEW YORK AND SOUTHERN NEW ENGLAND,
WHERE IT HAD A MAXIMUM AMOUNT OF A LITTLE OVER AN INCH OF RAINFALL.
THE CANADIAN REGIONAL MODEL HAD AROUND AN INCH AND A HALF OVER
SOUTHERN ONTARIO PROVINCE, WHILE A HALF INCH TO THREE QUARTERS OF AN
INCH SPILLED SOUTHWARD INTO THE ADIRONDACKS.  ANOTHER HALF INCH
CENTER WAS LOCATED OVER NORTHEASTERN PENNSYLVANIA TODAY.  THE
CANADIAN GLOBAL MODEL HAD LESS THAN A QUARTER INCH OVER THE ENTIRE
COUNTY WARNING AREA TODAY.  SO CLEARLY, THERE IS NO WAY OF COMING UP
WITH A GOOD MODEL CONSENSUS PRECIPITATION FORECAST FOR TODAY.  THE
BEST THAT CAN BE SAID, IS THAT THE AIR MASS WILL CONTINUE TO BE
CONDITIONALLY UNSTABLE , AND WITH THE UPPER-LEVEL GYRE PASSING
OVERHEAD, THERES LIKELY TO BE MORE SHOWERS AND THUNDERSTORMS,
ESPECIALLY THIS AFTERNOON.  BUT THE APPROACHING UPPER-LEVEL
VORTICITY MAXIMUM APPEARS TO BE TIED TO SHOWERS IN EASTERN
PENNSYLVANIA AT THE MOMENT, AND THIS COULD AFFECT THE SOUTHWESTERN
HALF OF THE COUNTY WARNING AREA DURING THE MORNING HOURS.  FOR THE
MOST PART, THE MODEL PROBABILITY OF PRECIPITATION VALUES ARE AGREED
THAT PRECIPITATION IS LIKELY TODAY.  THE AVIATION AND NESTED GRID
BASED VALUES WERE GENERALLY IN THE LIKELY CATEGORY, WHILE THE ETA
VALUES WERE SLIGHTLY LOWER, AROUND 50 PERCENT.  TUESDAYS ZONE
FORECASTS FOR TODAY HAD LIKELY PROBABILITIES, AND LIKELY RAINFALL
WILL BE FORECAST AGAIN ON THE NEXT RELEASE OF THE ZONES.  LITTLE
CHANGE IN MAXIMUM TEMPERATURE IS INDICATED BY THE NEW FORECAST
GUIDANCE AND THIS GUIDANCE WILL BE FOLLOWED CLOSELY.

IT SEEMS PROBABLE THAT THERE WILL BE A BREAK IN THE PRECIPITATION BY
LATE TONIGHT THROUGH THURSDAY.  THE UPPER-LEVEL SHORT WAVE WILL HAVE
MOVED EAST TONIGHT, SHIFTING THE FLOW ACROSS THE REGION TO A MORE
WESTERLY DIRECTION.  HOWEVER, A SECOND SHORT WAVE THAT TEMPORARILY
DEPRESSED THE RIDGE OVER THE NORTHERN ROCKIES THE PAST COUPLE OF
DAYS, WILL DIVE SOUTHEAST AND DEEPEN THE MAIN TROUGH TO OUR WEST
ONCE AGAIN.  THE FLOW WILL BEGIN TO BACK AROUND TO THE SOUTH
SOUTHWEST OVER THE NORTHEASTERN UNITED STATES LATE THURSDAY.
TUESDAYS ZONE FORECASTS INDICATE A CHANCE OF SHOWERS FOR TONIGHT
AND THURSDAY.  THE NEW FORECAST WILL GO WITH A CHANCE OF LINGERING
SHOWERS THIS EVENING, BUT WILL HAVE A DRY FORECAST AFTER MIDNIGHT.
MODEL PROBABILITY GUIDANCE VARIES A BIT FOR THURSDAY, BUT AVERAGES
AROUND 30 PERCENT ACROSS THE COUNTY WARNING AREA.  A LOW CHANCE OF
SHOWERS WILL BE MAINTAINED IN THE NEW ZONE FORECAST FOR THURSDAY.
GUIDANCE TEMPERATURES LOOK REASONABLE AND THE ZONES WILL STAY CLOSE
TO THIS GUIDANCE.

THE AVIATION AND CANADIAN GLOBAL MODEL HAD BEEN LATCHING ONTO A WAVE
IN THE SOUTH AND WERE ORIGINALLY BRINGING IT UP INTO THE NORTHEAST
ON THURSDAY.  THE CANADIAN GLOBAL, ETA, AND AVIATION STILL INDICATE
A WAVE FROM THE SOUTH, BUT BRING IT UP ABOUT A DAY LATER THAN
EARLIER RUNS HAD INDICATED.  THE ETA AND CANADIAN ARE THE QUICKEST,
AND HAVE PRECIPITATION POSSIBLY MOVING BACK INTO THE SOUTHEASTERN
PORTION OF THE AREA THURSDAY NIGHT.  THE AVIATION DOUSES THE REGION
WITH A PRETTY GOOD DUMP OF RAINFALL LATE FRIDAY INTO EARLY
SATURDAY.  THE CANADIAN HOLDS THE HEAVY PRECIPITATION OFF THE
ATLANTIC COAST.  FRIDAYS ZONE FORECAST HAD A CHANCE OF
PRECIPITATION IN THIS TIME FRAME, AND NO CHANGES WILL BE MADE.

.HYDROLOGICAL DISCUSSION...
THERE EXISTS AN UNUSUALLY HIGH FLOOD POTENTIAL FOR THIS TIME OF YEAR
DUE TO A VERY MOIST AND UNSTABLE TROPICAL AIR MASS. THE LATEST
GLOBAL FORECAST SYSTEM RUN INDICATES A CLOSED UPPER LOW WILL MOVE
VERY SLOWLY EASTWARD FROM NORTH OF LAKE HURON TO NORTH OF LAKE
ONTARIO BY HOUR 12 UNIVERSAL COORDINATION TIME FRIDAY.  THE LOW
LEVEL FLOW WILL CONTINUE FROM THE SOUTH AND SOUTHWEST THROUGH
THURSDAY MORNING...BUT WILL THEN SHIFT TO A MORE WESTERLY
DIRECTION.  THE TOTAL PRECIPITABLE WATER AT ALBANY WAS 2.2 INCHES ON
THE SOUNDING TUESDAY EVENING.  IT IS EXPECTED THAT THE PRECIPITABLE
WATER WILL DROP BY ALMOST AN INCH ONCE WE GET INTO LOW LEVEL FLOW
FROM THE WEST ON THURSDAY.  THE MAIN THREAT CONTINUES TO BE FROM
TRAINING HIGH PRECIPITATION CELLS WHICH DUMP TORRENTIAL RAIN OVER A
SMALL AREA IN A 1- TO 2-HOUR PERIOD, WITH RAPID FLOODING OF POORLY
DRAINED AREAS, PLUGGED CULVERTS, ETC.  AGAIN, LARGE PARKING AREAS
ARE PARTICULARLY VULNERABLE SUCH AS AROUND INDUSTRIAL PARKS,
SHOPPING CENTERS, AND BUSINESS DISTRICTS SUCH AS WHAT HAPPENED IN
SCHENECTADY ON MONDAY EVENING.  1-HR FLASH FLOOD GUIDANCE HAS VALUES
OF 1.6 TO 2.0 INCHES OVER MOST AREAS, BUT DRIER AREAS CAN TAKE A BIT
MORE.

RCK (HYDROLOGICAL DISCUSSION)

.ALY...NONE.

HEMMERICH (MAIN DISCUSSION)

CTZ001-013-MAZ001-025-NYZ032-033-038>043-047>054-058>061-063>066-
082>084-VTZ013>015-061000-

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE ALBANY NY
403 AM EDT WED AUG 6 2003

THIS HAZARDOUS WEATHER OUTLOOK IS FOR EASTERN NEW YORK AND ADJACENT
WESTERN NEW ENGLAND.

.DAY ONE...TODAY...NO SEVERE THUNDERSTORMS ARE FORECAST FOR TODAY.
HOWEVER, LOCALLY HEAVY RAINFALL IN SHOWERS AND THUNDERSTORMS IS
POSSIBLE, WHICH COULD TRIGGER LOCALIZED FLOODING IN MAINLY PAVED
AREAS, WHERE DRAINAGE IS POOR.

.DAYS TWO THOUGH SEVEN...
NO HAZARDOUS WEATHER IS EXPECTED AT THIS TIME.

.SPOTTER INFORMATION STATEMENT...
AT THIS TIME, IT IS NOT ANTICIPATED THAT SPOTTER ACTIVATION WILL BE
NECESSARY TODAY.