Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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000
FXUS63 KGRR 251720
AFDGRR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
1220 PM EST WED FEB 25 2015

LATEST UPDATE...
AVIATION

.SYNOPSIS...
ISSUED AT 330 AM EST WED FEB 25 2015

AN ARCTIC AIRMASS WILL REMAIN FIRMLY ENTRENCHED IN THE GREAT LAKES
REGION THROUGH FRIDAY. A WEAK SYSTEM WILL BRING A FEW LIGHT SNOW
SHOWERS TO FAR SOUTHERN LOWER MICHIGAN TONIGHT INTO THURSDAY
MORNING. HIGH PRESSURE WILL BUILD IN TO PRODUCE FAIR BUT COLD
WEATHER THURSDAY THROUGH SATURDAY. TEMPERATURES WILL FINALLY
UNDERGO A GRADUAL MODERATING TREND LATE THIS WEEKEND INTO EARLY
NEXT WEEK.

&&

.UPDATE...
ISSUED AT 1110 AM EST WED FEB 25 2015

THIS IS JUST A QUICK HEADS UP ON MY THINKING FOR TONIGHT. I AM
THINKING IT WILL SNOW TONIGHT (HIGH POP) NEAR AND SOUTH OF I-96.
THIS WILL NOT BE A HEAVY SNOW... MOSTLY AN INCH OR LESS BUT IT
WILL SNOW NONE THE LESS.

AFTER LOOKING AT THE NAM12...RAP13 AND HRRR IT SEEMS TO ME WHAT
WE WILL SEE IS A NARROW BAND OF SNOW DEVELOPING NEAR OR JUST NORTH
OF I-96 AROUND 9 TO 10 PM TONIGHT THAT WILL MOVE SLOWLY SOUTHWARD
(THIS IS SHOWN BY ALL THREE OF THESE MODELS) TO I-94 BY 5 AM. THIS
NARROW BAND IS THE RESULT OF SURFACE FGEN DUE THE RADIATIONAL COOLED
AIR OVER NORTHERN LOWER MICHIGAN COMPARED TO THE CLOUD COVERED AIR
(WHICH WILL NOT COOL) CREATING A THERMAL GRADIENT. THE BEST LIFT
IS JUST ABOVE THE IS NEAR 900 MB WHICH IS IN THE DGZ SO THIS WILL
MAXIMIZE THE SNOWFALL RATES. THIS IS GOING ON UNDER THE ENTRANCE
REGION OF THE UPPER JET SO WE GET DEEP MOISTURE AND DEEP LIFT
(WEAK BUT ALSO IN THE DGZ). AROUND MIDNIGHT THE DGZ OVER GRR IS
FROM 1000 FT TO 12000 FT....MORE THAN DEEP ENOUGH TO HELP THE SNOW
CAUSE. BOTTOM LINE IS I WILL INCREASE THE POP TO OVER 70% OVER THE
SOUTHERN 1/2 OF THE CWA THIS EVENING FOR THIS EVENT.

&&

.SHORT TERM...(TODAY THROUGH FRIDAY)
ISSUED AT 330 AM EST WED FEB 25 2015

FAIRLY TRANQUIL AND COLD WEATHER IS ANTICIPATED THROUGH THE SHORT
TERM FCST PERIOD. A FEW LIGHT SNOW SHOWERS AND FLURRIES WILL
LINGER INTO THIS MORNING BUT WITH VERY LITTLE TO NO ADDITIONAL
SNOW ACCUMULATION. MOST OF THE DAY WILL BE DRY BUT COLD WITH A MIX
OF SUN AND CLOUDS. MAX TEMPS WILL ONLY REACH 10 TO 15 DEGREES.

A WEAK SYSTEM MOVING ESE FROM THE NORTHERN PLAINS STATES EARLY
THIS MORNING WILL BRING A FEW LIGHT SNOW SHOWERS AND FLURRIES TO
OUR SOUTHERN FCST AREA NEAR TO MAINLY SOUTH OF I-96 TONIGHT INTO
THURSDAY MORNING... WITH VERY LIGHT SNOW ACCUMULATIONS OF UNDER AN
INCH.

BEYOND THAT HIGH PRESSURE WILL BUILD IN TO PRODUCE FAIR BUT COLD
WX THURSDAY AFTERNOON THROUGH FRIDAY. MAX TEMPS THURSDAY WILL
STRUGGLE TO REACH THE UPPER SINGLE DIGITS TO LOWER TEENS AND MINS
THURSDAY NIGHT WILL FALL TO BELOW ZERO ACROSS OUR AREA AS SKIES
CLEAR AND WITH LIGHT WINDS AND EXPANSIVE SNOW COVER IN PLACE. MAX
TEMPS FRIDAY WILL STRUGGLE TO REACH THE LOWER TO MIDDLE TEENS IN
SPITE OF LOTS OF SUN AFTER A VERY COLD START TO THE DAY.

.LONG TERM...(FRIDAY NIGHT THROUGH TUESDAY)
ISSUED AT 330 AM EST WED FEB 25 2015

UPPER AIR PATTERN SHIFT IS STILL FORECAST TO OCCUR BY THE 00Z MODEL
RUNS DURING THE LONG TERM. THE PERSISTENT UPPER TROUGH IS IN THE
PROCESS OF LIFTING OUT FRIDAY NIGHT. BY EARLY NEXT WEEK A SOUTHWEST
FLOW DEVELOPS ACROSS THE LOWER 48...FROM THE SOUTHWEST U.S. TO THE
GREAT LAKES.

THERE ARE TWO MAIN ITEMS TO KEEP AN EYE ON THROUGH THE PERIOD. THE
FIRST IS THE SNOW EVENT FOR SUNDAY AND SUNDAY NIGHT. IT REMAINS AN
EVENT WITH NO SURFACE LOW TO KEY ON. SNOW IS PRODUCED VIA A WEAK
FRONTAL BOUNDARY SLIPPING THROUGH THE AREA COUPLED WITH AN UPPER
LEVEL SHORT WAVE AND ISENTROPIC LIFT. IT APPEARS TO BE A 2-5 INCH
SNOW POTENTIALLY FOR THE SOUTHERN HALF OF THE FORECAST AREA. WE
STILL HAVE PLENTY OF TIME TO NAIL DOWN THE DETAILS WITH THIS SYSTEM.

THE SECOND SIGNIFICANT FEATURE TO KEEP AN EYE ON IS A SYSTEM NEXT
WEEK IN THE TUESDAY OR WEDNESDAY TIME FRAME. LOW CONFIDENCE IN THIS
TIME FRAME AS THE GFS IS QUICKER...BRINGING A DEEP LOW THROUGH THE
AREA ON TUESDAY. THE ECMWF AND CANADIAN ARE SLOWER AND BRING THE
SYSTEM THROUGH ON WEDNESDAY. AT THIS POINT...SIDING WITH THE ECMWF
AND CANADIAN AND THE SLOWER SYSTEM. THE SYSTEM TAPS GULF MOISTURE IN
DEEP SOUTHERLY FLOW. PRECIPITATION TYPE ISSUES COME INTO PLAY
TUESDAY NIGHT IN THE ECMWF/CANADIAN SOLUTIONS WITH +4 TO +6 850MB
AIR SURGING IN FROM THE SOUTH. THESE VALUES WOULD YIELD RAIN AS THE
PRECIP TYPE ALONG I94. MODELS ARE HAVING ISSUES WITH THIS SYSTEM AS
ITS DRIVEN BY A WAVE EJECTING OUT OF THE SOUTHWEST U.S. TROUGH. WE
WILL BE MONITORING TRENDS WITH THIS SYSTEM IN THE COMING DAYS.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z THURSDAY AFTERNOON)
ISSUED AT 1219 PM EST WED FEB 25 2015

OUR MAIN CONCERN WITH THE 18Z FCSTS IS DEALING WITH THE SNOW
COMING IN FROM LATE THIS AFTERNOON THROUGH THU MORNING. MID CLOUDS
ARE NOW STARTING TO STREAM IN OVER THE AREA...WITH SOME
DIURNAL/LAKE EFFECT CLOUD COVER NOW STARTING TO DEVELOP/MOVE
INLAND. WE EXPECT THAT ONLY KMKG WILL SEE THE LOWEST CONDITIONS
THIS AFTERNOON WITH 3500 FT CIGS AND SOME FLURRIES.

LIGHT SNOW WILL THEN BREAK OUT ACROSS THE TERMINALS THIS EVENING
INTO THE EARLY OVERNIGHT HOURS. MODELS ARE INDICATING THAT A LOCAL
BAND MAY SET UP AND POTENTIALLY IMPACT THE KGRR AREA FOR A SHORT
TIME THIS EVENING WITH SOME LOWER VSBYS. MVFR IS LIKELY WITH SOME
LOCAL IFR POSSIBLE.

A LIGHT SNOW WILL THEN LIKELY PERSIST OVERNIGHT AND INTO THU
MORNING. THIS WILL LAST LONGER ACROSS THE SOUTH. THE LOWER
CONDITIONS WILL ALSO BE ACROSS THE SOUTH CLOSER TO THE SYSTEM.
AGAIN...MVFR IS LIKELY WITH SOME IFR POSSIBLE AT TIMES. THIS WILL
GRADUALLY MOVE OUT THU MORNING. CONDITIONS WILL IMPROVE GRADUALLY
THU AFTERNOON.

&&

.HYDROLOGY...
ISSUED AT 224 PM EST TUE FEB 24 2015

CURRENTLY NO SUSPECTED ICE JAMS AND RIVER LEVELS ARE HOLDING RATHER
STEADY. FORECAST CALLS FOR BELOW FREEZING TEMPERATURES INTO NEXT
WEEK WITH OCCASIONAL SNOW OPPORTUNITIES. THE RISK OF FLOODING IS
FAIRLY LIMITED UNTIL A NOTABLE WARM-UP OR RAIN EVENT.

&&

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

$$

UPDATE...WDM
SYNOPSIS...LAURENS
SHORT TERM...LAURENS
LONG TERM...DUKE
AVIATION...NJJ
HYDROLOGY...CAS





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