Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 210506
AFDGRR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
1206 AM EST FRI NOV 21 2014

LATEST UPDATE...
AVIATION

.SYNOPSIS...
ISSUED AT 321 PM EST THU NOV 20 2014

LAKE EFFECT SNOW SHOWER WITH GUSTY WINDS AND BLOWING AND DRIFTING
SNOW WILL DIMINISH OVERNIGHT BUT IT WILL REMAIN VERY COLD WITH
LOWS IN THE BETWEEN 10 AND 15 MOST LOCATIONS...BUT CLOSER TO 20
NEAR THE LAKE MICHIGAN SHORE.

HIGH PRESSURE MOVING ACROSS THE AREA FRIDAY WILL FINALLY END THE
SNOW SHOWERS BY MID MORNING AND BRING SOME SUNSHINE DURING THE
AFTERNOON. IT WILL REMAIN COLD WITH HIGHS ONLY IN THE 20S.

A STORM SYSTEM FROM THE SOUTHERN PLAINS WILL BRING WARMER AIR INTO
THE REGION THIS WEEKEND AND THAT WILL MEAN FREEZING RAIN CHANGING
TO RAIN SATURDAY MORNING THEN LIGHT RAIN THE REST OF THE DAY
SATURDAY. ON SUNDAY AS THE SYSTEM MOVES THROUGH THE AREA EXPECT
RAIN TO BE HEAVY AT TIMES WITH GUSTY WINDS. MONDAY THE COLD AIR
COMES BACK AND RAIN SHOWERS CHANGE TO SNOW SHOWERS. ONCE IN PLACE
AGAIN THE COLD AIR AND SNOW SHOWERS ARE EXPECTED TO CONTINUE MOST
OF THANKSGIVING WEEK.

&&

.UPDATE...
ISSUED AT 901 PM EST THU NOV 20 2014

WE ARE IN THE PROCESS OF CHIPPING AWAY AT THE WINTER WEATHER
ADVISORY THIS EVENING BY TAKING OUT THE FOUR NRN COUNTIES IN THE
ADVISORY. WE WILL BE LEAVING THE REMAINDER OF THE ADVISORY UP FOR
THE TIME BEING THINKING THERE IS A GOOD CHANCE THAT THE REMAINDER
OF IT WILL BE ABLE TO BE CANCELLED WITH THE OVERNIGHT FCST PACKAGE.

LATEST RADAR TRENDS AND OBSERVATIONS INDICATE A DOWNWARD TREND IN
THE COVERAGE AND INTENSITY OF THE SNOW SHOWERS UP NORTH THIS
EVENING. THE BEST BAND OF SNOW SHOWERS EXTENDS FROM OTTAWA
COUNTY...AND INTO SRN KENT...FAR NE ALLEGAN...AND FAR NW BARRY
COUNTY AS OF 02Z. THIS BAND IS SHIFTING SOUTH AND WEST WITH TIME
AS THE MEAN LOW LEVEL FLOW BECOMES MORE NW TONIGHT.

ALL SNOW BANDS WILL DIMINISH IN INTENSITY OVERNIGHT AS THE UPPER
CYCLONIC FLOW BEGINS TO LIFT OUT OF THE AREA RESULTING IN LOWERING
INVERSION HEIGHTS AND DIMINISHING LOW LEVEL CONVERGENCE. WE WILL
SEE SOME ACCUMULATION WITH THIS BAND SINKING SOUTH EARLY ON...BUT
THE ACCUMULATION POTENTIAL WILL DIMINISH OVERNIGHT.

UPDATE ISSUED AT 553 PM EST THU NOV 20 2014

UPDATED TO END THE ADVISORY EARLY FOR THE EASTERN COUNTIES. KGRR-
88D HAS SHOWN A STEADY DECREASE IN AREAL COVERAGE EAST OF GRAND
RAPIDS AND THIS TREND SHOULD CONTINUE AS THE UPPER TROUGH AXIS
MOVES THROUGH. THE REST OF THE FORECAST REMAINS UNCHANGED.

&&

.SHORT TERM...(THIS EVENING THROUGH SATURDAY NIGHT)
ISSUED AT 321 PM EST THU NOV 20 2014

THE TWO BIG ISSUES FOR THIS FORECAST IS WHEN WILL THE SNOW SHOWERS
FINALLY END AND WILL WE HAVE A SIGNIFICANT AMOUNT OF FREEZING RAIN
SATURDAY MORNING?

A POWERFUL 160 TO 180 KNOT PACIFIC JET CORE IS MOVING TOWARD THE
WEST COAST AS I WRITE THIS. THAT JET CORE UNDERCUTS THE UPPER
RIDGE OVER THE WEST COAST AND IN TURN BOOTS THE DEEP UPPER LOW
OVER THE EASTERN UNITED STATES OVER THE NORTH ATLANTIC. THIS
ALLOWS THE ASSOCIATED SYSTEM WITH THAT STRONG PACIFIC JET CORE TO
DIG INTO THE SOUTHWESTERN UNITED STATES DURING THE DAY ON
SATURDAY. A NEGATIVE TILT TROUGH COMES OUT OF THAT FOR
SUNDAY...WHICH IS WHAT CREATES THE WARM UP AND RAIN OVER THE
WEEKEND. MODEL AGREEMENT ON FROM RUN TO RUN AND MODEL TO MODEL
HAS BEEN EXCELLENT THE PAST FEW DAYS. SO THERE IS LITTLE QUESTION
WE WILL GET THE WARM AIR SURGE THIS WEEKEND...MELTING MOST OF THE
SNOW COVER.

THE CORE OF THE COLD AIR DOES NOT COME IN UNTIL EARLY FRIDAY
MORNING AND THE UPPER JET AXIS DOES NOT CROSS SOUTHWEST MICHIGAN
UNTIL MID MORNING FRIDAY. SO THE LAKE EFFECT SNOW SHOWERS WILL
CONTINUE THROUGH THE NIGHT. HOWEVER AS WINDS DIMINISH THIS EVENING
AND THE SHORTWAVE MOVING THROUGH THE AREA DEPARTS...WINDS WILL TURN
MORE TO THE NORTHWEST AND THAT WILL REORGANIZE THE SNOW SHOWERS TO
BE MORE MOSTLY NEAR US-131 ONCE THE SUN SETS. I COULD STILL SEE 3
TO 4 INCHES OF NEW SNOW FALL IN SOME AREAS FROM THESE SNOW BEFORE
THIS ALL COMES TO AN END BY MID MORNING FRIDAY.

WITH HIGH PRESSURE MOVING ACROSS THE AREA FRIDAY I WOULD EXPECT
SOME SUNSHINE TO RETURN BY EARLY AFTERNOON. WE ARE STILL IN THE
SHALLOW COLD AIR WHICH MEANS A STRONG SHALLOW INVERSION... SO
TEMPERATURES WILL REMAIN COLD...EVEN WITH THE SUN COMING OUT.

FRIDAY NIGHT INTO SATURDAY MORNING THE DEEP MOISTURE RETURNS AS
THE SOUTHERN STREAM SYSTEMS HEADS FOR SOUTHWEST MICHIGAN. THE
1000 TO 850 MOISTURE TRANSPORT VECTORS ARE AMID THIS WAY. THE LOW
LEVEL JET OF 40 TO 45 KNOTS BRINGS THE 900 TO 800 MB DEW POINTS
INTO THE LOWER 40S BY SATURDAY MORNING OVER LOWER MICHIGAN.
PRECIPITABLE WATER VALUES RISE TO NEAR .7 INCHES BY SATURDAY
MORNING...THAT WILL HELP THE CAUSE OF BRINGING MOISTURE BACK INTO
THE REGION. ALL OF THIS TELLS ME WE WILL LIKELY SEE PRECIPITATION
SATURDAY MORNING (STARTING BEFORE SUNRISE) AND THAT WILL CONTINUE
INTO THE EVENING. SINCE THE MID LEVEL TEMPERATURES RISE WELL ABOVE
FREEZING BEFORE THE SURFACE TEMPERATURES DO... LIKELY WE WILL SEE
A FEW HOURS OF MIXED FREEZING RAIN...SLEET AND SNOW CHANGE TO
FREEZING RAIN INTO THE MID MORNING HOURS OF SATURDAY. BY MID DAY
SATURDAY TEMPERATURES SHOULD BE ABOVE FREEZING ACROSS THE AREA SO
LIGHT RAIN WILL CONTINUE INTO THE EVENING. WITH THE WARM AIR
COMING IN OVER THE SNOW PACK I WOULD EXPECT SOME FOG TO (I DID NOT
YET PUT THIS IN OUR GRIDS THROUGH).

.LONG TERM...(SUNDAY THROUGH THURSDAY)
ISSUED AT 321 PM EST THU NOV 20 2014

TEMPERATURES AT THE START OF THE PERIOD WILL BE MUCH WARMER THAN
THEY ARE CURRENTLY...BUT STILL RIGHT AROUND NORMAL. HIGHS SUNDAY
WILL BE IN THE MID 40S AND IT LOOKS LIKE WE/LL SEE QUITE A BIT OF
RAIN. LOW PRESSURE MOVING NORTHEAST FROM THE SOUTHERN PLAINS WILL
SPREAD RAIN OVER THE CWA SUNDAY. THIS WILL CONTINUE SUNDAY NIGHT.
TOTAL RAINFALL NEAR AN INCH ARE POSSIBLE AND THIS MAY RESULT IN SOME
MINOR FLOODING. IT/S ALSO GOING TO ADD WEIGHT TO ROOFS AS THE
SNOW PACK ABSORBS IT. TEMPS WILL ONLY FALL A COUPLE OF DEGREES SUNDAY
NIGHT BUT REMAIN IN THE 40S. AFTER THE LOW MOVES BY LATE SUNDAY
NIGHT...COLDER AIR WILL BEGIN TO FLOW IN BEHIND IT. HIGHS MONDAY
WILL PROBABLY OCCUR BETWEEN MIDNIGHT AND 6 AM WITH TEMPS FALLING
THROUGH THE DAY.

A VERY DEEP LONG WAVE TROUGH WILL DEVELOP OVER THE MISSISSIPPI
VALLEY BY TUESDAY ENSURING A SUPPLY OF COLD AIR FLOWS OVER THE GREAT
LAKES. H8 TEMPS BY 0Z TUESDAY ARE PROGD TO BE NEAR -10C AND FALL TO
AROUND -15C BY TUESDAY MORNING. LAKE EFFECT SNOW SHOWERS WILL
DEVELOP BY MONDAY EVENING AND CONTINUE THROUGH THURSDAY AND
ACCUMULATIONS ARE EXPECTED.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z FRIDAY NIGHT)
ISSUED AT 1205 AM EST FRI NOV 21 2014

LAKE EFFECT SNOW SHOWERS WILL BE ENDING WITH VFR BY 08Z. WINDS WILL
DIMINISHING AS WELL AND GOING SOUTHWEST FRIDAY AFTERNOON AROUND 10
KNOTS.

&&

.MARINE...
ISSUED AT 321 PM EST THU NOV 20 2014

WINDS AND WAVES WILL REMAIN STRONG ENOUGH FOR SMALL CRAFT
ADVISORIES INTO FRIDAY MORNING. WINDS AND WAVES WILL LET UP AS THE
SURFACE HIGH MOVES ACROSS THE AREA FRIDAY BUT ONCE THE HIGH MOVES
TO THE EAST SOUTHERLY WINDS WILL INCREASE TO 20 TO 30 KNOTS FRIDAY
NIGHT RESULTING IN THE NEED FOR ANOTHER SMALL CRAFT ADVISORY.


&&

.HYDROLOGY...
ISSUED AT 321 PM EST THU NOV 20 2014

WE ARE STILL MONITORING THE FLOOD THREAT OVER THE WEEKEND AS
AROUND A INCH OF RAIN IS EXPECTED TO FALL OVER OUR CURRENT SNOW
PACK. THE LATEST GUIDANCE FROM THE NCRFC INDICATES NONE OF OUR
RIVERS WILL RISE TO OR ABOVE FLOOD STAGE BUT WE MAY WELL HAVE SOME
MINOR URBAN AND SMALL STREAM FLOODING NONE THE LESS.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...WINTER WEATHER ADVISORY UNTIL 7 AM EST THIS MORNING FOR MIZ050-
     056-057-064-065-071-072.

LM...SMALL CRAFT ADVISORY UNTIL 7 AM EST THIS MORNING FOR LMZ844>849.

&&

$$

UPDATE...NJJ
SYNOPSIS...WDM
SHORT TERM...WDM
LONG TERM...93
AVIATION...OSTUNO
HYDROLOGY...WDM
MARINE...WDM






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