Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 210730
AFDGRR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
330 AM EDT TUE APR 21 2015

LATEST UPDATE...
SYNOPSIS/SHORT TERM/LONG TERM/MARINE

.SYNOPSIS...
ISSUED AT 330 AM EDT TUE APR 21 2015

A FAIRLY WIDESPREAD AREA OF LOW PRESSURE WILL REMAIN IN CONTROL OF
THE ENTIRE STATE...AND MUCH OF THE REGION FOR A GOOD PORTION OF THE
WEEK. THIS LOW WILL BRING OCCASIONAL CHANCES FOR RAIN/SNOW SHOWERS
THROUGH THURSDAY. MUCH BELOW AVERAGE TEMPERATURES CAN BE EXPECTED
ALSO. CONDITIONS MAY DRY OUT OVER THE WEEKEND...HOWEVER TEMPS WILL
REMAIN COOL.

&&

.SHORT TERM...(TODAY THROUGH THURSDAY)
ISSUED AT 330 AM EDT TUE APR 21 2015

OUR FOCUS OF THE FORECAST TODAY WILL BE ON THE PCPN CHCS AND P-TYPE
ISSUES WITH THE COLD UPPER LOW IN PLACE. UPPER LOW WILL REMAIN IN
CONTROL THROUGH THE PERIOD. UPPER CYCLONIC FLOW WILL HOLD IN
PLACE...KEEPING THE COOL TEMPS ALOFT IN PLACE ALSO.

RAIN HAS BEEN THE DOMINATE P-TYPE OVERNIGHT TONIGHT. WE HAVE BEEN
RECEIVING A COUPLE OF REPORTS OF SOME SNOW AND GRAUPEL STARTING TO
MIX IN AT TIMES ALONG AND NORTH OF I-96. FREEZING LEVELS/WET BULB
ZERO HEIGHTS ARE COMING DOWN...BUT STILL SUPPORT MAINLY RAINFALL.
HEAVIER CONVECTIVE BURSTS ARE ALLOWING FOR SOME OF THE WINTRY MIX TO
BE OBSERVED.

PERIODS OF SHOWERS CAN BE EXPECTED FOR TODAY AND RIGHT ON THROUGH
THE DAY ON WED. THE BETTER CHCS FOR PCPN WILL BE FOUND ACROSS THE
NORTH...A LITTLE CLOSER TO THE UPPER LOW THAT IS CENTERED JUST NORTH
OF THE STATE. WE SHOULD SEE MAINLY RAIN TODAY AS HIGH ENOUGH MELTING
LAYERS REMAIN IN PLACE MOST OF THE DAY AND WITH SFC TEMPS INTO THE
40S.
WE WILL SEE MORE COLDER AIR ADVECT IN FROM THE NORTH LATER TODAY
THAT WILL ALLOW MORE SNOW TO MIX IN EVENTUALLY LATE TODAY AND
TONIGHT.

WE ARE EXPECTING A LULL IN THE SHOWER ACTIVITY FOR TONIGHT AS WE
LOSE THE DIURNAL COMPONENT TO THE INSTABILITY UNDER THE LOW. A
SLIGHT CHC HAS TO REMAIN IN HOWEVER AS WE WILL HAVE SPOKES OF ENERGY
ROTATING IN AROUND THE UPPER LOW. PCPN IS LIKELY TO CHANGE OVER TO
MAINLY LIGHT SNOW SHOWERS AS THE MELTING LAYER/WET BULB ZERO HEIGHTS
DROP EVEN MORE WITH COLDER AIR CONTINUING TO FUNNEL IN.

WE WILL SEE A GENERAL REPEAT OF THE PATTERN THEN FOR WED/WED
NIGHT...WITH A LITTLE LESS OF A THREAT OF PCPN AS THE MAIN TROUGH
AXIS WITH THE UPPER LOW WILL SHIFT EAST OF THE AREA. WE WILL STILL
SEE POTENTIAL SHORT WAVES MOVE THROUGH THAT WILL COMBINE WITH
DIURNAL INSTABILITY AND BRING AT LEAST A LOW CHC OF A FEW SHOWERS.
SNOW MAY END UP BEING THE DOMINATE P-TYPE AT NIGHT WITH A CHANGE TO
MIXED RAIN/SNOW DURING THE DAY WITH DIURNAL HEATING. THE THREAT OF
PCPN WILL DROP A BIT MORE FOR THU...HOWEVER A SMALL CHC WILL REMAIN
WITH THE JET CORE STILL SOUTH AND WEST OF THE AREA.

.LONG TERM...(THURSDAY NIGHT THROUGH MONDAY)
ISSUED AT 330 AM EDT TUE APR 21 2015

IN GENERAL A RATHER UNEVENTFUL LONG TERM PERIOD WITH BELOW NORMAL
TEMPERATURES AND LITTLE OR NO PRECIPITATION. WE WILL BE IN NORTHWEST
UPPER FLOW ON THE WRN EDGE OF THE BROAD UPPER LOW OVER NEW
ENGLAND... WITH SURFACE RIDGING AND A DRY AIR MASS PREVAILING AT THE
SURFACE.

A HIGH RISK OF FROST AND FREEZING TEMPERATURES EXISTS ON THURSDAY
NIGHT AS SKIES CLEAR WITH SURFACE RIDGE BUILDING IN. THERE IS ALSO A
THREAT ON FRIDAY NIGHT ALTHOUGH CONFIDENCE IS LOWER SINCE GUIDANCE
HINTS AT POSSIBILITY OF HIGH CLOUDS FROM PLAINS SYSTEM IMPACTING THE
AREA. COULD EVEN BE A RISK OF FROST THROUGH THE REMAINDER OF THE
LONG TERM PERIOD WITH COOL/DRY AIR MASS HANGING AROUND.

ECMWF SUGGESTS THE POSSIBILITY OF SOME LIGHT RAIN IMPACTING AREAS
SOUTH OF I-96 LATE FRIDAY NIGHT INTO SATURDAY AS THE NRN EDGE OF THE
PRECIP SHIELD RELATED TO THE PLAINS SYSTEM BRUSHES THE AREA. FOR NOW
HAVE SIDED WITH THE DRY LOOK OF THE GFS WITH THE IDEA THAT THE
CONFLUENT FLOW ALOFT AND DRY LOW LEVEL EAST FLOW WILL FEND OFF ANY
PRECIPITATION IN SRN LWR MI.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z TUESDAY NIGHT)
ISSUED AT 1148 PM EDT MON APR 20 2015

FAIRLY HIGH CONFIDENCE THAT WE WILL STAY ABOVE FUEL ALTERNATES AND
MAY IN FACT EVEN REMAIN VFR THROUGH 12Z. EXPECT LIGHT RAIN TO
REDEVELOP LATE TUESDAY MORNING/EARLY AFTERNOON PRIMARILY AT
NORTHERN TERMINALS. EXPECT LITTLE VSBY RESTRICTIONS...BUT CIGS ARE
A BIT LESS CERTAIN. CURRENTLY ADVERTISE CIGS LOWERING TO AROUND
025 AREAWIDE BUT COULD SEE FUEL ALTS BELOW 020 REALIZED AT MKG AND
GRR.

&&

.MARINE...
ISSUED AT 330 AM EDT TUE APR 21 2015

WE WILL BE HOLDING ON TO THE SMALL CRAFT ADVISORY FOR MUCH OF THE
PERIOD. IT IS POSSIBLE THAT THE ADVISORY MAY NEED TO BE EXTENDED AT
SOME POINT. A FAIRLY STIFF GRADIENT WILL REMAIN OVER THE AREA TODAY.
WINDS OF 30+ KNOTS WILL BE WITHIN REACH OF BEING MIXED DOWN OVER THE
WATER...HOWEVER THE COLD LAKE WILL LIKELY LIMIT THE GUSTS A BIT.

&&

.HYDROLOGY...
ISSUED AT 1156 AM EDT MON APR 20 2015

WIDESPREAD RAINFALL THROUGH 8 AM THIS MORNING PRODUCED 0.50 TO 0.75
INCHES ACROSS MOST OF THE GRAND AND MUSKEGON RIVER BASINS. FURTHER
SOUTH ACROSS THE KALAMAZOO RIVER BASIN...RAINFALL AMOUNTS WERE
HIGHER IN THE 0.75 TO 1.00 INCH RANGE. AS EXPECTED...GRADUAL RIVER
RISES HAVE BEGUN ON MOST AREA RIVERS. GENERAL HYDRO THINKING HAS NOT
CHANGED MUCH...MOSTLY WITHIN BANK RISES ARE EXPECTED. A FEW SITES
COULD EXCEED BANKFULL. BUT WITH RAIN TODAY AND TONIGHT BEING OF THE
SCATTERED AND LIGHT VARIETY...SIGNIFICANT FLOODING IS NOT EXPECTED.

FORECAST RAINFALL TODAY AND TONIGHT IS IN THE 0.10 TO 0.25 INCH
RANGE. EVEN LIGHTER PRECIP AMOUNTS ARE EXPECTED TUESDAY
INTO WEDNESDAY. A SLIGHT CHANCE OF LIGHT RAIN AND SNOW WILL LINGER
WEDNESDAY NIGHT THROUGH THURSDAY NIGHT. BUT MAINLY DRY AND CHILLY
WEATHER IS EXPECTED TOWARD THE END OF THE WEEK.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
LM...SMALL CRAFT ADVISORY UNTIL 6 PM EDT WEDNESDAY FOR LMZ844>849.

&&

$$

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





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