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000
FXUS63 KGRR 061733
AFDGRR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
1233 PM EST FRI DEC 6 2013

LATEST UPDATE...
AVIATION

.SYNOPSIS...
ISSUED AT 332 AM EST FRI DEC 6 2013

COLD AIR IS EXPECTED TO REMAIN IN PLACE THROUGH THE WEEKEND. THERE
WILL BE SOME LAKE EFFECT SNOW SHOWERS THROUGH SATURDAY. NO
SIGNIFICANT ACCUMULATIONS ARE EXPECTED. MOST OF THE AREA SHOULD SEE
LIGHT SNOW ACCUMULATIONS LATE SUNDAY THROUGH MONDAY AS A WAVE OF LOW
PRESSURE MOVES THROUGH THE AREA.

COLDER AIR WILL MOVE IN DURING THE EARLY PORTION OF NEXT WEEK.
CONDITIONS LOOK A BIT MORE FAVORABLE FOR LAKE EFFECT SNOW
ACCUMULATIONS NEXT WEEK...ESPECIALLY ACROSS THE WESTERN HALF OF THE
AREA.

&&

.UPDATE...
ISSUED AT 1128 AM EST FRI DEC 6 2013

I UPDATED THE FORECAST TO SHOW HIGHER PROBABILITIES OF LIGHT SNOW
SHOWERS WEST OF US-131 BASED ON RADAR RETURNS...SURFACE OBS (BIV
1 1/2-4SM -SN/ MKG 2-4SM -SN)...LAKE ENHANCED IR IMAGE LOOPS AND
USING THE OMEGA AND RH FROM THE LATEST RAP MODEL IN THE 0-2KM
LAYER. THE LATEST RAP MODEL SUGGESTS THE AREA OF BEST LIFT WILL
SHIFT SOUTH THIS AFTERNOON FROM WHITEHALL TO SOUTH HAVEN NOW... TO
HOLLAND TO BENTON HARBOR BY MID AFTERNOON. INLAND EXPECT JUST
FLURRIES (I PUT FLURRIES IN THE GRIDS TOO). AS ALWAYS IN THESE
SITUATIONS EVEN THE HIGH RES MODELS ARE HAVING A PROBLEM
FORECASTING THIS TYPE OF SNOW SHOWER ACTIVITY.

I STILL EXPECT THE BETTER ACCUMULATIONS TONIGHT INTO SATURDAY SO I
UPDATED THOSE GRIDS TO SHOW HIGHER PROBABILITIES. STILL
ACCUMULATIONS SHOULD BE LESS THAN 2 INCHES IN MOST PLACES.

ELSEWHERE AND OTHERWISE THE FORECAST IS ON TRACK.

&&

.SHORT TERM...(TODAY THROUGH SUNDAY)
ISSUED AT 332 AM EST FRI DEC 6 2013

THE MAIN FOCUS OF THE SHORT TERM PORTION OF THE FCST REMAINS LAKE
EFFECT TRENDS THROUGH THE PERIOD WITH COLD AIR EXPECTED TO REMAIN IN
PLACE. NO REAL CHANGES HAVE BEEN MADE WITH THE FCST AS MODELS ARE
SHOWING GOOD RUN TO RUN CONSISTENCY.

LAKE EFFECT HAS BEEN SLOW TO GET STARTED WITH THIS COLD AIR
MASS...AND THAT CONTINUES TO BE THE CASE THIS MORNING. SOME FLURRIES
ARE BEING REPORTED AT KCAD JUST NORTH OF THE CWFA...BUT NOTHING IN
THE CWFA AS OF 08Z THIS MORNING. THE LACK OF MOISTURE DEPTH AND LACK
OF LOW LEVEL CONVERGENCE UNDER FAIRLY ROBUST SUBSIDENCE WITH THE
ENTRANCE REGION OF THE STRONG UPPER JET IS OVERCOMING THE HEALTHY
OVER LAKE INSTABILITY.

WE DO EXPECT TO SEE A FEW SNOW SHOWERS DEVELOP TODAY. ONGOING CAA
WILL HELP A BIT TO LOWER THE DGZ INTO THE LIMITED MOISTURE LAYER A
BIT BETTER. THE AFOREMENTIONED LIMITING FACTORS WILL KEEP ANY SNOW
SHOWERS UNDER CONTROL TODAY. THE ONGOING CAA WILL LIMIT THE AMOUNT
OF WARMING FOR TEMPS TODAY. HIGHS SHOULD NOT CLIMB ABOVE THE UPPER
20S AFTER WE LOSE A FEW DEGREES THIS MORNING.

WE CONTINUE TO ANTICIPATE AN UPTICK IN LAKE EFFECT SNOW SHOWER
ACTIVITY FOR TONIGHT AND EARLY SAT MORNING. THIS UPTICK IS EXPECTED
TO BE THE RESULT OF A SHORT WAVE/PV ANOMALY CURRENTLY OVER NM THIS
MORNING LIFTING TO THE NE OVER THE AREA TONIGHT. INVERSION HEIGHTS
WILL BUMP UP TO AROUND 5K FEET OR SO. AT THE SAME TIME...A BIT OF
MID LEVEL MOISTURE WILL TRY TO HELP SNOW SHOWER GENERATION WITH A
SEEDER FEEDER TYPE OF SCENARIO. THERE WILL BE ABOUT 4-6K FT OF DRY
AIR IN BETWEEN THE LAYERS...SO IT IS NOT A GUARANTEE THIS WILL
ABSOLUTELY HELP. THE DGZ WILL BE SATURATED QUITE A BIT WHICH WILL
HELP FOR THE SNOW CAUSE. WNW FLOW FAVORED AREAS WILL SEE THE BEST
CHC OF SNOW SHOWERS AND SOME ACCUMULATIONS. LOW LEVEL CONVERGENCE IS
STILL LACKING...SO WE DO NOT EXPECT SNOW AMOUNTS TO GET OUT OF HAND.

WE WILL SEE THE LAKE EFFECT SNOW SHOWERS THEN GRADUALLY DIMINISH IN
COVERAGE AND INTENSITY DURING THE DAY ON SAT. THE NM SHORT WAVE WILL
EXIT THE AREA AND SUBSIDENCE WILL TAKE CONTROL ONCE AGAIN. INVERSION
HEIGHTS ARE EXPECTED TO LOWER TO AROUND 3K FEET...BEFORE LOW LEVEL
MOISTURE IS EXPECTED TO DISSIPATE WITH A STRONG ARCTIC SFC RIDGE
MOVING DIRECTLY OVERHEAD. THIS WILL ALLOW FOR A COLD SAT NIGHT WITH
SOME CLEARING LIKELY.

THE CLEARING AND BREAK IN THE SNOW SHOWERS WILL BE SHORT LIVED. WE
WILL SEE ADDITIONAL SHORT WAVE ENERGY EJECT OUT FROM THE WRN U.S.
TROUGH AND APPROACH THE AREA SUN AFTERNOON. SOME MOISTURE FROM THE
STRONG STORM SYSTEM EXPECTED ACROSS THE SE STATES WILL WRAP INTO
THIS WAVE AS IT IS PASSING ACROSS THE STATE. THE MOISTURE IS NOT
THAT RICH AS THE BEST MOISTURE WILL REMAIN WELL SE OF THE AREA WITH
THE MAIN BAROCLINIC/FRONTAL ZONE ACROSS THE SE PORTION OF THE
COUNTRY. FORCING IS LIMITED TOO THIS FAR NORTH WITH THE MAIN
ISENTROPIC ASCENT REMAINING WELL SOUTH AND EAST. THIS LOOKS LIKE A
LIGHT SNOW EVENT WHERE MOST OF THE AREA WILL SEE AN INCH OR TWO OF
SNOW ACCUMULATION.

.LONG TERM...(SUNDAY NIGHT THROUGH THURSDAY)
ISSUED AT 332 AM EST FRI DEC 6 2013

THE SYNOPTIC SYSTEM FOR SUNDAY NIGHT CONTINUES TO LOOK LESS
IMPRESSIVE WITH EACH MODEL RUN. WEAK/BAGGY SFC LOW PRESSURE PATTERN
PASSES ACROSS LOWER MI WITH ONLY AROUND ONE TENTH OF AN INCH OF QPF.
NO DECENT/AMPLIFIED SHORTWAVE IS PRESENT ALOFT...AND INSTEAD IT IS
JUST A SHEARED OUT/ELONGATED VORTICITY PATTERN.

THERE IS ALSO THE ISSUE OF A POTENTIAL MID LEVEL DRY SLOT SWEEPING
IN WHICH COULD LEAD TO MORE OF A LIGHT FREEZING RAIN/DRIZZLE THREAT
SUNDAY NIGHT RATHER THAN LIGHT SNOW. WILL KEEP LIKELY POPS FOR LIGHT
SNOW OVER THE ENTIRE AREA FOR NOW BUT IF THE TRENDS CONTINUE THEN
THE FREEZING PRECIP THREAT MAY NEED TO BE ADDED IN LATER FORECASTS.

COLD ADVECTION FOLLOWS ON MONDAY BEHIND THE WEAK EXITING SYSTEM BUT
THE REALLY COLD ARCTIC AIR DOES NOT ARRIVE UNTIL TUESDAY OR TUESDAY
NIGHT.  IT IS THE CLIPPER SYSTEM TRACKING ACROSS LAKE SUPERIOR WHICH
BRINGS IN THE COLD AIR AND PERHAPS A BETTER RISK OF SOME
ACCUMULATING LAKE EFFECT SNOW. EVEN THIS IS QUESTIONABLE HOWEVER
SINCE THE CORE OF THE UPPER JET DOES NOT DIP SOUTH OF THE STATE AND
MOISTURE IS RATHER SHALLOW/LIMITED.

THE LAKE EFFECT SNOW SHOWER THREAT IS EXPECTED TO DIMINISH THURSDAY
AS SURFACE RIDGING BUILDS IN.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z SATURDAY AFTERNOON)
ISSUED AT 1233 PM EST FRI DEC 6 2013

A MIX OF VFR AND MVFR CEILINGS CAN BE EXPECTED OVER THE NEXT 24
HOURS. THE BULK OF THE MVFR WILL BE DOWN WIND FROM LAKE MICHIGAN...
WITH NW OR WNW FLOW. THE MVFR CONDITIONS SHOULD BE MOST PERSISTENT
AT AZO...WITH VFR AND OCCASIONAL MVFR EXPECTED FOR THE REMAINDER
OF THE TAF SITES.

THERE WILL ALSO BE LIGHT SNOW SHOWERS COMING OFF THE LAKE. MOST
VSBYS WILL BE REDUCED INTO THE MVFR RANGE...HOWEVER A FEW ISOLATED
SNOW SHOWERS MAY BRING VSBYS DOWN INTO THE IFR RANGE. ONCE
AGAIN...WITH THE NW FLOW...AZO SHOULD SEE MORE FREQUENT SNOW
SHOWERS THEN THE REST OF THE TAF SITES.  THE HIGHEST IMPACT SNOW
SHOWERS SHOULD OCCUR FROM ROUGHLY 04Z TO 14Z SATURDAY WHEN THE
BEST LOW LEVEL MOISTURE IS REALIZED.

&&

.MARINE...
ISSUED AT 332 AM EST FRI DEC 6 2013

WE ARE EXTENDING THE SMALL CRAFT ADVISORY FOR THE ENTIRE NEARSHORE
THROUGH 06Z SUN WITH THIS FCST PACKAGE. WINDS WILL COME DOWN TO
AROUND 15 TO 20 KNOTS TODAY AND REMAIN THERE THROUGH SAT. THE
ONSHORE FLOW AND UNSTABLE CONDITIONS WITH THE COLD AIR COMING IN
OVER THE LAKE WILL KEEP WAVES ABOVE 4 FEET THROUGH SAT. THERE SHOULD
BE A BREAK SAT NIGHT AND EARLY SUN.


&&

.HYDROLOGY...
ISSUED AT 332 AM EST FRI DEC 6 2013

THE ONLY CONCERN WITH HYDROLOGY REMAINS THE THREAT FOR ICE
DEVELOPMENT OVER THE NEXT WEEK. ARCTIC COLD AIR EXPECTED OVER THE
AREA THROUGH MOST OF THE NEXT WEEK WILL HELP ICE DEVELOPMENT. AS THE
ICE DEVELOPS...WE WILL BE MONITORING THE POTENTIAL FOR ICE JAMS TO
FORM.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
LM...SMALL CRAFT ADVISORY UNTIL 1 AM EST SUNDAY FOR LMZ844>849.

&&

$$

UPDATE...WDM
SYNOPSIS...NJJ
SHORT TERM...NJJ
LONG TERM...MEADE
AVIATION...JK
HYDROLOGY...NJJ
MARINE...NJJ