Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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000
FXUS63 KGRR 210349
AFDGRR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
1149 PM EDT MON APR 20 2015

LATEST UPDATE...
AVIATION

.SYNOPSIS...
ISSUED AT 330 PM EDT MON APR 20 2015

A STALLED STORM SYSTEM OVER THE NORTHERN GREAT LAKES WILL KEEP
SHOWERS AND UNSEASONABLY COLD WEATHER THROUGH A GOOD PART OF THIS
WEEK. THE SHOWERS MAY BE MIXED WITH SNOW OR TURN TO SNOW AT TIMES
TUESDAY NIGHT INTO THURSDAY. ANY ACCUMULATIONS WILL BE MINOR.
FREEZING TEMPERATURES ARE EXPECTED EACH MORNING STARTING ON
WEDNESDAY.

&&

.SHORT TERM...(THIS EVENING THROUGH WEDNESDAY NIGHT)
ISSUED AT 330 PM EDT MON APR 20 2015

THE MAIN ISSUES ARE THE PRECIPITATION THREAT...THE RISK FOR SNOW
TUESDAY NIGHT INTO WEDNESDAY NIGHT AND THE GUSTY WINDS TONIGHT INTO
WEDNESDAY. OUR STALLED LOW PRESSURE SYSTEM WILL CONTINUE BRING
COLDER AIR INTO THE REGION INTO WEDNESDAY. SHORTWAVES ROTATING
AROUND THE STALLED SYSTEM WILL KEEP SHOWERS GOING THROUGH THE
SHORT TERM. WITH THE LAKE TEMPERATURE NEAR 3C... AND 850 TEMPS
FALLING TO NEAR -8C.... THAT IS MARGINAL FOR LAKE EFFECT BUT GIVEN
THERE IS ENOUGH MOISTURE IN THE 950 TO 700 MB LAYER THROUGH THIS
TIME PERIOD SHOWERS WILL CONTINUE AS WELL AS GUSTY WINDS. BY
TUESDAY NIGHT IT GETS COLD ENOUGH FOR MIXER RAIN AND SNOW AND THAT
THREAT CONTINUES INTO WEDNESDAY NIGHT.

SOME NOTE WORTHY ASPECTS TO OUR STORM SYSTEM... BASED ON THE
WESTERN REGION ENSEMBLE SITUATIONAL AWARENESS TABLE... A LOW
PRESSURE SYSTEM AS DEEP AS THIS ONE IS (984 MB AT 8 AM THIS
MORNING) HAS A RETURN PERIOD THAT IS LESS FREQUENT THAN ONCE IN 30
YEARS. HAVING 850 MB TEMPERATURES FALL INTO THE -8C TO -10C RANGE
OVER WESTERN LOWER MICHIGAN AND LAKE MICHIGAN DURING AROUND THE
21ST AND 22ND OF APRIL OCCURS ONLY ONCE IN 5 YEARS. HAVING THE 700
MB TEMPERATURE BELOW -16C HAPPENS LESS THAN ONCE IN 10 YEARS. SO
MY POINT IS THIS EVENT IS ACTUALLY A RATHER RARE EVENT FOR THIS
TIME OF YEAR IN THE GREAT LAKES.

IT SHOULD BE NOTED THE COLD TEMPERATURES (925/850/700/500 MB) FORECAST
BY THE GFS...ECMWF..THE ENSEMBLES OF BOTH...THE GEFS AND NAEFS
HAVE VERY PERSISTENT RUN AFTER RUN FOR MORE THAN A WEEK. MY POINT
HERE IS WE CAN TRUST THAT IT REALLY WILL GET AS COLD AS WE ARE
FORECASTING IT TO BE. WHICH MEANS WHEN THE 850 TEMPS FALL BELOW -6C
TOMORROW EVENING... SNOW WILL BE MORE LIKELY THAN RAIN AS A
PRECIPITATION TYPE.

.LONG TERM...(THURSDAY THROUGH MONDAY)
ISSUED AT 330 PM EDT MON APR 20 2015

UNSEASONABLY COOL WEATHER WILL CONTINUE THURSDAY WITH THE UPPER
TROUGH AXIS IN PLACE OVER THE EASTERN GREAT LAKES REGION AND DEEP
CYCLONIC FLOW. SCATTERED RAIN SHOWERS WILL LINGER THURSDAY AND MAY
BE MIXED AT TIMES WITH WET SNOW FLAKES PARTICULARLY ACROSS HIGHER
ELEVATIONS OF OUR NORTHERN FCST AREA.

THE UPPER TROUGH WILL SHIFT FURTHER EAST THURSDAY NIGHT AS A SFC
RIDGE BEGINS TO BUILD IN. THIS WILL LIKELY SET THE STAGE FOR A
COLDER NIGHT DEPENDING ON EXTENT AND TIMING OF CLEARING AS THE RIDGE
BEGINS TO BUILD IN. THERE IS POTENTIAL FOR WIDESPREAD TEMPS IN THE
25 TO 30 DEGREE RANGE BY EARLY FRIDAY MORNING SO FROST/FREEZE ISSUES
ARE CERTAINLY A CONCERN FOR LATE WEEK.

THE SFC HIGH PRESSURE RIDGE WILL BRING FAIR BUT COOL WEATHER FRIDAY
INTO SATURDAY. MAX TEMPS BY FRIDAY SHOULD REACH THE UPPER 40S TO
LOWER 50S WITH MIN TEMPS FRIDAY NIGHT IN THE 20S TO AROUND 30
DEGREES. TEMPERATURES WILL UNDERGO A SLOW MODERATING TREND FOR THE
WEEKEND INTO EARLY NEXT WEEK WITH FAIR WX EXPECTED TO CONTINUE WITH
THE SFC RIDGE REMAINING IN CONTROL OF THE WX PATTERN.

&&

.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 PM EDT MON APR 20 2015

I EXTENDED THE AREA COVERED BY THE SCA TO COVER THE ENTIRE NEAR
SHORE. I ALSO CONTINUED IT THROUGH WEDNESDAY AFTERNOON. WITH OUR
SYSTEM STALLED OVER THE GREAT LAKES MOST OF THE WEEK WE WILL SEE A
CONTINUATION OF 15 TO 25 KNOT WINDS FROM THE SOUTHWEST INTO
TUESDAY THEN NORTHWEST TUESDAY NIGHT THROUGH A GOOD PART OF THE
REST OF THE WEEK.


&&

.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...WDM
SHORT TERM...WDM
LONG TERM...LAURENS
AVIATION...TJT
HYDROLOGY...EBW
MARINE...WDM






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