000
FXUS63 KGRR 071146
AFDGRR

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

LATEST UPDATE...
AVIATION

.SYNOPSIS...
ISSUED AT 327 AM EST SAT DEC 7 2013

LAKE EFFECT SNOW SHOWERS WILL GRADUALLY DIMINISH THROUGH THIS
EVENING. SOME ADDITIONAL LIGHT SNOW ACCUMULATIONS WILL BE
LIKELY...ESPECIALLY FOR OTTAWA AND ALLEGAN COUNTIES. THE AREA WILL
SEE A BREAK IN THE SNOW SHOWERS LATER TONIGHT AND EARLY SUNDAY
BEFORE LIGHT SNOW SPREADS ACROSS THE AREA LATER ON SUNDAY. SOME
FREEZING DRIZZLE WILL BE POSSIBLE ACROSS SOUTHERN AREAS SUNDAY NIGHT
BEFORE MORE LAKE EFFECT IS GENERATED ON MONDAY. COLD AIR WILL REMAIN
ENTRENCHED ACROSS THE AREA.

&&

.SHORT TERM...(TODAY THROUGH MONDAY)
ISSUED AT 327 AM EST SAT DEC 7 2013

THE MAIN FOCUS OF THE FCST IN THE SHORT TERM REVOLVES AROUND THE
SYSTEM EXPECTED TO MOVE ACROSS THE AREA FROM LATE SUN INTO MON
MORNING. MOST OF THE FCST REMAINS UNCHANGED...HOWEVER WE DID ADD
SOME FREEZING DRIZZLE ACROSS THE SRN COUNTIES FOR LATER SUN NIGHT.

WE WILL SEE LAKE EFFECT SNOW SHOWERS CONTINUE TODAY INTO THIS
EVENING WITH ANOTHER INCH OR SO POSSIBLE ACROSS OTTAWA AND ALLEGAN
COUNTIES. WE DO EXPECT HOWEVER THAT THEY WILL SLOWLY DIMINISH IN
COVERAGE AND INTENSITY THROUGH THIS PERIOD. THE SHORT WAVE MOVING
ACROSS THE AREA AND HELPING TO BOOST INVERSION HTS TO AROUND 6K FT
PER THE KGRR VWP WILL BE EXITING OVER THE NEXT COUPLE OF HOURS.
INVERSION HTS WILL DROP TO AROUND 3-4K FT WITH SUBSIDENCE MOVING IN
AND LOW LEVEL CONVERGENCE WILL WEAKEN.

THE PERIOD FROM THIS EVENING INTO THE FIRST PORTION OF SUN SHOULD BE
RATHER QUIET. THIS WILL OCCUR AS SHORT WAVE UPPER RIDGING WILL BUILD
OVER THE AREA AS THE UPPER JET STREAK ACROSS THE ROCKIES GETS READY
TO SUPPORT ANOTHER STORM OVER THE SE U.S..

WE WILL SEE THE CHC OF PCPN /ALL IN THE FORM OF SNOW/ BEGIN TO
INCREASE SUN AFTERNOON...AND THEN PEAK OVERNIGHT SUN NIGHT. THIS
SNOW DOES NOT LOOK TO BE A BIG SNOW PRODUCER. THE GOOD MOISTURE
TRANSPORT WILL REMAIN WELL TO OUR SOUTH...ASSOCIATED ON THE SOUTH
SIDE OF THE JET STREAK MOVING IN TO OUR SOUTH. WE WILL SEE WEAK
MOISTURE TRANSPORT AT BEST AHEAD OF THE SHORT WAVE THAT WILL MOVE
THROUGH. MID LEVEL MIXING RATIOS ARE AROUND 2 G/KG DURING THE
EXPECTED TIME OF THE PCPN.

THE PCPN DURATION WILL ONLY LAST ABOUT 6-12 HOURS...HIGHEST UP
NORTH. THE HIGHEST AMOUNTS WILL BE UP NORTH AS THE SRN PORTION OF
THE AREA LOOKS TO BECOME DRY SLOTTED BETWEEN 06-09Z. WE COULD 1 TO 3
INCHES OR SO UP NORTH...WITH AN INCH OR TWO AT BEST SOUTH. THE SOUTH
ALSO HAS THE POTENTIAL FOR FREEZING DRIZZLE AS THE DRY SLOT MOVES
IN...AND COULD LAST UNTIL 12-15Z WHEN THE COLDER AIR COMES IN AND
SATURATES THE DGZ ONCE AGAIN. THIS COULD IMPACT THE MON MORNING
COMMUTE.

COLDER AIR WILL RUSH IN ON MON WITH H850 TEMPS DROPPING TO -15C TO
-18C COMING IN. THIS WILL HELP TO TRANSITION ANY PCPN OVER TO LAKE
EFFECT SNOW SHOWERS. THE MOISTURE IS NOT EXPECTED TO BE
EXCEPTIONALLY DEEP AS THE UPPER CYCLONIC FLOW DOES NOT BECOME FIRMLY
ESTABLISHED OVER THE AREA. THIS DOES LOOK TO BE A WRLY FLOW...SO ALL
AREAS ALONG AND WEST OF U.S.-131 WILL BE IN LINE FOR SOME ACCUMS ON
MON.

.LONG TERM...(MONDAY NIGHT THROUGH FRIDAY)
ISSUED AT 327 AM EST SAT DEC 7 2013

THE LONG TERM PERIOD WILL FEATURE MUCH BELOW TEMPERATURES WITH
OCCASIONAL LAKE EFFECT SNOW SHOWERS. OVERALL SNOW ACCUMULATIONS DO
NOT LOOK PARTICULARLY IMPRESSIVE SINCE THE AIR MASS REMAINS RATHER
DRY AND THE DEPTH OF THE MIXED LAYER WILL BE SHALLOW WITH INVERSION
HEIGHTS GENERALLY AT OR BELOW 5K FEET.

PROBABLY THE BEST CHANCE OF ACCUMULATING LAKE EFFECT SNOW /DRY AND
FLUFFY/ WILL BE TUESDAY INTO WEDNESDAY AS A CLIPPER SYSTEM PASSES
ACROSS LAKE SUPERIOR AND DRIVES A REINFORCING SFC COLD FRONT THROUGH
THE REGION. INITIALLY THIS WOULD BE A SOUTHWEST FLOW EVENT ON
TUESDAY IMPACTING AREAS FROM BIV/GRR TO THE NORTH... FOLLOWED BY
NORTHWEST FLOW TUESDAY NIGHT INTO WEDNESDAY CAUSING BANDS TO SHIFT
AND REALIGN.

H8 TEMPS OF -15 TO -20C COME IN BEHIND THE FRONT ON TUESDAY...
ALTHOUGH THIS IS NOT REALLY A WHOLE LOT COLDER THAN THE AIR MASS WE
ARE CURRENTLY IN. THE CORE OF THE COLDEST AIR WITH H8 TEMPS NEAR
-25C REMAINS TO OUR NORTH TUESDAY INTO WEDNESDAY. THAT SAID HIGH
TEMPERATURES ON WEDNESDAY MAY STRUGGLE TO REACH 20 DEGREES.

THERE IS SOME UNCERTAINTY IN LATER PERIODS REGARDING HOW QUICK THE
COLD AIR LIFTS OUT... BUT GUIDANCE DOES SUGGEST SOME MODERATION IN
TEMPERATURES TOWARD THE END OF THE WEEK.

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z SUNDAY MORNING)
ISSUED AT 646 AM EST SAT DEC 7 2013

AREAS OF MVFR CIGS/VSBYS TODAY WITH THE SCATTERED LAKE EFFECT SNOW
SHOWERS. VFR EXPECTED TONIGHT.

&&

.MARINE...
ISSUED AT 327 AM EST SAT DEC 7 2013

WE WILL MAINTAIN THE SMALL CRAFT ADVISORY INTO THE OVERNIGHT HOURS
TONIGHT...ALTHOUGH IT WILL BE POSSIBLE THAT IT COULD BE CANCELLED A
LITTLE EARLY. WINDS WILL GRADUALLY COME DOWN STARTING LATER THIS
MORNING AND AFTERNOON. THERE WILL BE A LAG IN THE WAVES COMING DOWN
DUE TO THE COLD AIR MOVING OVER THE LAKE. THERE SHOULD BE A BREAK IN
THE WINDIER CONDITIONS FOR TONIGHT AND EARLY SUNDAY. ANOTHER SMALL
CRAFT ADVISORY WILL LIKELY BE NEEDED BEGINNING LATER ON SUN AND
BEYOND.


&&

.HYDROLOGY...
ISSUED AT 327 AM EST SAT DEC 7 2013

WE CONTINUE TO MONITOR THE THREAT FOR ICE DEVELOPMENT AND POTENTIAL
ICE JAMS OVER THE NEXT WEEK. THE TREND OVER THE PAST COUPLE OF DAYS
HAS BEEN FOR THE COLD AIR TO NOT BE QUITE AS COLD AS A FEW DAYS AGO.
THAT SAID...AVERAGE MAX/MIN TEMPS WILL STILL SUPPORT ICE
DEVELOPMENT. PEOPLE NEAR SOME OF THE TYPICAL LOCATIONS FOR ICE JAMS
WILL NEED TO KEEP VIGILANCE.

&&

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

&&

$$

SYNOPSIS...NJJ
SHORT TERM...NJJ
LONG TERM...MEADE
AVIATION...MEADE
HYDROLOGY...NJJ
MARINE...NJJ