Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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000
FXUS63 KGRR 260501
AFDGRR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
1201 AM EST THU FEB 26 2015

LATEST UPDATE...
AVIATION

.SYNOPSIS...
ISSUED AT 310 PM EST WED FEB 25 2015

A SYSTEM PASSING SOUTH OF MICHIGAN WILL BRING LIGHT SNOW TO THE
AREA FROM LATER THIS EVENING INTO EARLY THURSDAY. A LARGE POLAR
HIGH PRESSURE SYSTEM WILL THEN CONTROL THE WEATHER OVER SOUTHWEST
MICHIGAN THROUGH SATURDAY MORNING. VERY COLD TEMPERATURES ARE
EXPECTED THROUGH SATURDAY MORNING. A SLOW WARMING TREND BEGINS
SATURDAY. BY SUNDAY ENOUGH MOISTURE REACHES MICHIGAN TO BRING SNOW
TO THE AREA AS A WEAK SYSTEM PASSES WELL SOUTH OF MICHIGAN.

&&

.SHORT TERM...(THIS EVENING THROUGH FRIDAY NIGHT)
ISSUED AT 310 PM EST WED FEB 25 2015

I EXPECT LIGHT SNOW TO DEVELOP NEAR INTERSTATE 96 IN A NARROW BAND LATE
THIS EVENING (AROUND 10 PM OR SO). THAT NARROW AREA OF LIGHT SNOW
WILL SLOWLY SPREAD SOUTH AND MERGE WITH AN AREA OF SNOW MOVING
SOUTHEAST FROM WISCONSIN AND ILLINOIS AFTER MIDNIGHT AS I HEADS
TOWARD INTERSTATE 94. SNOWFALL FROM THIS EVENT WILL BE
LIGHT...MOSTLY AND INCH OR LESS. ARCTIC HIGH PRESSURE BUILDS IN
BEHIND THE SYSTEM FOR THURSDAY NIGHT INTO FRIDAY NIGHT SO FOR THE
MOST PART IT WILL JUST BE VERY COLD. WE MAY NEED WIND CHILL
HEADLINES THURSDAY NIGHT AND FRIDAY NIGHT.

THE SYSTEM THIS EVENING IS RATHER CURIOUS IN THAT EVEN THOUGH THE
PRIMARY SYSTEM PASSES WELL SOUTH AND WEST OF MICHIGAN TONIGHT...
BEING UNDER JET EXIT REGION WE STILL GET DEEP LIFT OVER MOST OF
SOUTHWEST LOWER MICHIGAN DURING THE LATE EVENING AND EARLY MORNING
HOURS. DURING THIS TIME THE DGZ IS RATHER DEEP AND NEARLY
SATURATED FROM NEAR THE SURFACE TO 12,000 FT AT MIDNIGHT.
MEANWHILE WE GET A DIFFERENTIAL COOLING BOUNDARY THAT SETS UP JUST
NORTH OF INTERSTATE 96 WHICH RESULTS IN A SURFACE FGEN BAND THAT
MOVES NEARLY DUE SOUTH FROM INTERSTATE 96 AT AROUND MIDNIGHT TO
NEAR INTERSTATE 94 BY 4-5 AM OR SO. WHEN THE JUXTAPOSITION OF THE
DEEP (WEAK )LIFT AND THE SURFACE FGEN COME TOGETHER WE GET A
NARROW BAND OF SNOW SHOWERS NEAR INTERSTATE 96 AS A RESULT (BY
MIDNIGHT). THIS AREA WILL SLOWLY MOVE SOUTH OVER TIME...MERGING
WITH THE SYSTEM PASSING SOUTH OF MICHIGAN BY MORNING. MOST AREAS
WILL SEE LESS THAN AN INCH OF SNOW FROM THIS EVENT.

ALL OF THIS MOVES OUT BY MID MORNING THURSDAY AND THAT ALLOW A
LARGE POLAR HIGH TO BUILD IN WITH MOSTLY NORTHERLY SURFACE WINDS.
THAT WILL KEEP ANY LAKE EFFECT SNOW BANDS OFF SHORE TOMORROW. WITH
NEARLY CLEAR SKIES THURSDAY NIGHT INTO FRIDAY MORNING TEMPERATURES
IN MOST AREAS WILL FALL TO BETWEEN 5 AND 25 BELOW ZERO. LIKELY WE
WILL NEED A WIND CHILL ADVISORY FOR THAT.

.LONG TERM...(SATURDAY THROUGH WEDNESDAY)
ISSUED AT 310 PM EST WED FEB 25 2015

TWO ITEMS OF INTEREST REMAIN IN THE LONG TERM PORTION OF THE FCST.
THESE ITEMS ARE SYSTEMS THAT WILL POTENTIALLY BRING SOME
ACCUMULATING SNOW TO THE AREA. A PATTERN SHIFT IS STILL EXPECTED
WHERE WILL WILL NOT BE SEEING WAVES OF BRUTALLY COLD AIR AS MUCH AS
THE PAST FEW WEEKS.

THE FIRST POTENTIAL OF ACCUMULATING SNOW WILL COME DURING THE SAT
NIGHT/SUN TIME FRAME AFTER A QUIET SAT. THE EXACT TIMING AND
POSITION IS A LITTLE UNCERTAIN YET. IT DOES APPEAR IT WILL BE
CENTERED AROUND THE LATTER PART OF SAT NIGHT TO SUN MORNING. AS
MENTIONED BEFORE...WE DO NOT SEE MUCH OF AN UPPER WAVE OR SFC
REFLECTION OF A LOW. INSTEAD...WE WILL BECOME UNDER THE INFLUENCE OF
THE LFQ REGION OF A DEVELOPING UPPER JET STREAK DOWNSTREAM OF THE
UPPER LOW DIGGING ACROSS THE SW. IN ADDITION...WE WILL SEE AN INFLUX
OF LOW LEVEL MOISTURE ADVECT IN WITH RETURN FLOW TAPPING THE GULF.

WE WILL SEE A RELATIVELY QUIET PERIOD ON SUN NIGHT THROUGH MON NIGHT
WITH SOMEWHAT MILDER TEMPS HIGH PRESSURE WILL CONTROL THE WEATHER
FROM SUN NIGHT THROUGH MON NIGHT. THERE IS A SMALL CHC OF SOME LAKE
EFFECT NEAR THE LAKESHORE THOSE DAYS. THE OVER LAKE INSTABILITY IS
MARGINAL WITH H850 TEMPS ONLY AROUND -10C OR SO. THE NRN BRANCH OF
THE JET IS NEVER REALLY EXPECTED TO DROP SOUTH OF THE AREA. THIS
WILL KEEP INVERSION HEIGHTS LOW WITH LIMITED MOISTURE DEPTH.

THE SECOND SYSTEM OF INTEREST WILL BE COMING IN FOR THE PERIOD ON
TUE/TUE NIGHT NEXT WEEK. A LOT OF UNCERTAINTY REMAINS WITH THIS
SYSTEM WITH REGARDS TO PCPN AMOUNTS...P-TYPE...AND TIMING. WE WILL
BE SEEING A PIECE OF ENERGY EJECT FROM THE DEVELOPING SW U.S. LOW
AND HEADING TOWARD THE AREA. AT THE SAME TIME...A NRN STREAM SYSTEM
WILL MOVE TOWARD THE AREA. THE BIG UNCERTAINTY COME WITH HOW
MUCH...IF ANY PHASING TAKES PLACE. NOT REALLY A LOT OF RUN-TO-RUN
CONTINUITY WITH THIS SYSTEM. IF IT PHASES...WE COULD SEE A LOT MORE
PCPN WITH MIXED P-TYPES. IF IT REMAINS UNPHASED...WE WILL SEE LESS
PCPN AND SNOW AS THE MAIN P-TYPE.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z THURSDAY NIGHT)
ISSUED AT 1159 PM EST WED FEB 25 2015

OCCASIONAL LIGHT SNOW WILL BRING VSBYS OF 2-4 MILES OVERNIGHT AND
THURSDAY MORNING MAINLY SOUTH AND EAST OF GRR. THE LIGHT SNOW WILL
END BETWEEN 14Z AND 18Z THURSDAY FROM NORTHWEST TO SOUTHEAST.
MAINLY MVFR CONDITIONS TONIGHT AND THURSDAY MORNING SOUTH AND EAST
OF GRR ARE EXPECTED TO IMPROVE TO PRIMARILY VFR CONDITIONS AFTER
18Z THURSDAY.

&&

.HYDROLOGY...
ISSUED AT 310 PM EST WED FEB 25 2015

RIVER LEVELS ARE HOLDING STEADY WELL BELOW BANKFULL WITH ONLY MINOR
FLUCTUATIONS AT SEVERAL SITES. RIVER SURFACES ARE MOSTLY TO ENTIRELY
ICE/SNOW COVERED AND FLOW UNDERNEATH THE ICE DOES NOT APPEAR TO BE
IMPEDED BY ICE JAMS AT ANY GAUGE SITE CURRENTLY. THE RISK OF
FLOODING WILL REMAIN RATHER LIMITED UNTIL A WARM UP OR SIGNIFICANT
RAINFALL COMES AROUND.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
LM...NONE.
&&

$$

SYNOPSIS...WDM
SHORT TERM...WDM
LONG TERM...NJJ
AVIATION...MEADE
HYDROLOGY...CAS





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