000
FXUS63 KGRR 070502
AFDGRR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
1202 AM EST SAT DEC 7 2013

LATEST UPDATE...
AVIATION

.SYNOPSIS...
ISSUED AT 338 PM EST FRI DEC 6 2013

THE COLDEST EARLY DECEMBER TEMPERATURES IN MANY YEARS ARE EXPECTED
DURING THE MIDDLE OF NEXT WEEK.

SNOW SHOWERS WILL PREVAIL WITH 1 TO 2 INCHES OF ACCUMULATION NEAR
AND WEST OF US-131 THROUGH SATURDAY EVENING. FROM SUNDAY NIGHT
INTO MONDAY EXPECT A GENERAL SNOWFALL OF 1 TO 3 INCHES. LAKE
EFFECT SNOW SHOWERS ARE EXPECTED MIDDAY MONDAY THROUGH THURSDAY
WITH SIGNIFICANT ACCUMULATIONS POSSIBLE WEST OF US-131.

&&

.UPDATE...
ISSUED AT 1003 PM EST FRI DEC 6 2013

WE HAVE ISSUED AN UPDATE THIS EVENING TO INCREASE SNOW TOTALS A
LITTLE FOR TONIGHT FOR THE OTTAWA AND ALLEGAN COUNTY AREAS.

LAKE EFFECT SNOW SHOWER ACTIVITY IS ONGOING THIS EVENING...
ESPECIALLY ACROSS THE OTTAWA AND ALLEGAN COUNTY AREAS WITH THE WNW
FLOW. SNOW SHOWERS HAVE NOT GOT OUT OF HAND THUS FAR...AND WE
SHOULD BE SEEING THE PEAK OF THE SNOW SHOWER INTENSITY FROM NOW
THROUGH THE NEXT FEW HOURS AS THE SHORT WAVE MOVES THROUGH FROM
THE SW. INVERSION HEIGHTS/CLOUD TOPS SEEM TO BE AROUND 6K FEET PER
THE KGRR VWP. THIS IS A TAD HIGHER THAN FCST SOUNDINGS ARE
SHOWING. AS THE SHORT WAVE IS EXPECTED TO BE EXITING THE CWFA JUST
AFTER 06Z TONIGHT...SNOW SHOWER INTENSITY AND COVERAGE SHOULD
DIMINISH SOME.

&&

.SHORT TERM...(THIS EVENING THROUGH SUNDAY NIGHT)
ISSUED AT 328 PM EST FRI DEC 6 2013

OUR FORECAST ISSUES FOR THE SHORT TERM ARE LAKE EFFECT SNOWFALL
TONIGHT INTO SATURDAY. OUR NEXT ISSUE IS THE SYNOPTIC SYSTEM
SUNDAY NIGHT IS OUR NEXT SYSTEM TO WATCH.

WE CONTINUE TO MONITOR THE LAKE EFFECT SNOWFALL WHICH HAS ALREADY
GIVEN MUSKEGON AN INCH OF SNOW (18Z OBS). A PV ANOMALY ASSOCIATED
WITH AN NORTHERN STREAM WAVE WILL ENHANCE THE SNOWFALL TONIGHT
INTO SATURDAY. NOTHING MUCH HAS CHANGED IN THE MODELS FOR THIS
LAKE EFFECT EVENT... MOISTURE IS VERY SHALLOW NOT MUCH MORE THAN
5000 FT BUT AS THE COLDER AIR CONTINUES TO COME IN THIS EVENING
THE DGZ ACTIVATES (HELPED BY A NORTHERN STREAM SHORTWAVE (PV
ANOMALY). THE CIPS ANALOGS SHOW 4 TO 5 INCHES BY SATURDAY EVENING.
SO SINCE WE ALREADY HAVE REPORTS OF SNOW ACCUMULATING AND THE LAKE
EFFECT IS EXPECTED TO INCREASE TONIGHT... SEEMS GOOD TO HAVE HIGH
POPS AND AN INCH OR TWO OF ACCUMULATION TONIGHT WITH ANOTHER INCH
TOMORROW. IF THE CIPS ARE CORRECT... WE COULD SEE EVEN MORE. ALL
OF THIS SHOULD SLOWLY END SATURDAY EVENING AS THE SURFACE HIGH
MOVES ACROSS THE AREA.

THE SYSTEM COMING OUT OF THE SW CONUS HAS BEEN RATHER CONSISTENT
ON THE MODELS AND SOUTHWEST LOWER MICHIGAN IS UNDER THE POLAR JET
SO WITH WILL BE ISENTROPIC LIFT EVENT. THE MOISTURE AVAILABLE FOR
THIS IS LIMITED... ONLY 3 G/KG NEAR 700 MB... SO SNOWFALL WILL BE
LIMITED BUT I SEE NO REASON WHY WE SHOULD NOT GET 1 TO 3 INCHES
FROM IT. AS A RESULT I INCREASED POPS TO 80 PCT OVER MUCH OF THE
AREA. THERE COULD BE A DRY SLOT BUT IT SEEMS NOW THAT WILL BE
OVER OUR SE CWA. LATER FORECASTS MAY NEED TO PUT SOME FREEZING
DRIZZLE IN THAT AREA AT LEAST PART OF SUNDAY NIGHT.

.LONG TERM...(MONDAY THROUGH FRIDAY)
ISSUED AT 328 PM EST FRI DEC 6 2013

THE SYNOPTIC SNOWS SHOULD BE WINDING DOWN MONDAY MORNING...BUT THEN
THE LAKE EFFECT FOLLOWS ON IT/S HEELS INTO THE AFTERNOON.  WITH THE
ARCTIC AIR PUSHING IN MAX TEMPS WILL PROBABLY OCCUR IN THE
MORNING...WITH FALLING TEMPS INTO THE AFTERNOON.  THIS ARCTIC AIR
SHOULD PRODUCE THE AFTERNOON SCATTERED LAKE EFFECT SNOW SHOWERS WITH
INVERSION HEIGHTS AROUND 5K FT.  WE SHOULD SEE A LULL IN THE LES
MONDAY NIGHT WITH SHORT WAVE RIDGING SHOWN...BUT THEN IT SHOULD KICK
UP AGAIN TUESDAY AND CONTINUE INTO WEDNESDAY WITH A COUPLE OF SHORT
WAVES PASSING THROUGH.  THE LAKE EFFECT APPEARS TO DIMINISH FOR THE
REST OF THE WORK WEEK AS HIGH PRESSURE MOVES ACROSS THE OH VALLEY.

THE OTHER SIGNIFICANT LONG TERM STORY WILL BE THE ARCTIC AIR
ITSELF.  WE HAVE BEEN TALKING ABOUT THE COLDEST EARLY DEC PERIOD
SINCE 2000...AND THIS STILL LOOKS VERY LIKELY.  GOOD AGREEMENT IN
THE MODELS SHOW THE THERMAL TROUGH WILL BE OVER THE GREAT LAKES BY
WEDNESDAY WITH H8 TEMPS OF -20 TO -21C.  THIS SHOULD HOLD MAX TEMPS
IN THE UPPER TEENS TO AROUND 20 TUESDAY AND WEDNESDAY.  WIND CHILL
READINGS SHOULD BE BELOW ZERO AT TIMES FROM LATE MONDAY NIGHT INTO
EARLY THURSDAY MORNING.  THIS TYPE OF ARCTIC AIR ONLY PENETRATES
INTO OUR AREA IN EARLY DEC ABOUT ONCE EVERY 20 YEARS...SIGNIFICANT
FOR SURE.

WE SHOULD HAVE A MODERATION OF TEMPS INTO THU/FRI...BUT THE MODELS
DISAGREE TO WHAT EXTENT THE WARM AIR REACHES LOWER MI.  HAVE 20S
THU...AND LOW TO MID 30S FOR FRI...BUT WE WILL CONTINUE TO MONITOR
TRENDS AND TWEAK ACCORDINGLY.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z SATURDAY NIGHT)
ISSUED AT 1158 PM EST FRI DEC 6 2013

MVFR CONDITIONS WILL PREVAIL OVERNIGHT AS LAKE EFFECT STRATUS
WITH CEILINGS 2500 TO 3000 FEET AGL COVERS MUCH OF SOUTHWEST LOWER
MICHIGAN. SNOW SHOWERS SHOULD BE LIGHT AND CONFINED TO AREAS FROM
MKG TO GRR AND AZO. WINDS WILL BE NORTHWEST AOB 10 KNOTS.

&&

.MARINE...
ISSUED AT 238 PM EST FRI DEC 6 2013

LITTLE REASON TO CHANGE OUR FORECAST OR HEADLINES AT THIS POINT.
NORTHWEST WINDS OF 15 TO 25 KNOTS WILL KEEP WAVES IN THE 4 TO 7
FOOT RANGE INTO SATURDAY BEFORE WINDS DIMINISH LATE IN THE DAY
ALLOWING WAVE HEIGHTS TO ALSO DIMINISH.


&&

.HYDROLOGY...
ISSUED AT 238 PM EST FRI DEC 6 2013

WE WILL CONTINUE TO MONITOR THE ICE JAM THREAT AS THE COLD WEATHER
PERSISTS. THE GENERAL SNOWFALL SUNDAY NIGHT INTO MONDAY MAY
FACILITATE ICE FORMATION ON AREA RIVERS.

&&

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

&&

$$

UPDATE...NJJ
SYNOPSIS...WDM
SHORT TERM...WDM
LONG TERM...WDM
AVIATION...OSTUNO
HYDROLOGY...WDM
MARINE...WDM