Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 170539
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
139 AM EDT Tue Apr 17 2018

LATEST UPDATE...
Aviation

.SYNOPSIS...
Issued at 320 PM EDT Mon Apr 16 2018

Low pressure that dumped sleet and freezing rain on southwest Lower
Michigan will slowly move away from the region tonight and Tuesday.
A brief period of dry weather will develop before another round of
rain and snow moves into the picture late Wednesday into Thursday.

Temperatures will remain cold for this time of year but begin warming
by the end of the week. We`ll be in the 50s over the weekend.

&&

.UPDATE...
Issued at 1101 PM EDT Mon Apr 16 2018

Based on radar, surface obs and satellite trends the snow shower
coverage supports higher POPs. Still looks like an inch or less
will work out for most locations. Products were updated.

UPDATE Issued at 947 PM EDT Mon Apr 16 2018

Scattered snow showers will persist for much of the night with
local impacts possible. They will be driven by the cyclonic flow
through the convective layer. Temperatures with this airmass are
low enough to tap the moisture from Lake MI...which will enhance
some of the snow showers. Will keep the wording for snow showers
in the forecast.

&&

.SHORT TERM...(This evening through Wednesday)
Issued at 320 PM EDT Mon Apr 16 2018

Forecast concerns deal with lingering light snow tonight and then
the approach of the next system Wednesday.

Regional radar shows light snow falling over the state and this
should continue off and on tonight. The surface low that produced
the strong winds and sleet/ice has moved to Ontario. However, the
upper low will linger for another day or so and snow showers can be
expected tonight before diminishing Tuesday.

A narrow ridge between the departing low and the next system will
move across the state Tuesday night. A low in Kansas will move
across the cwa Wednesday. Some warmer air will move north into the
state and light rain will develop late in the day.

Temperatures will remain cold through Tuesday as highs tomorrow will
struggle to reach the mid 30s. However, temperatures will warm into
the mid 40s Wednesday.

.LONG TERM...(Wednesday night through Monday)
Issued at 320 PM EDT Mon Apr 16 2018

Fairly high confidence with the track and timing and even QPF
amounts for the sfc low that tracks just south of Lower Michigan on
Wednesday night. The only issue to be determined is precip type. We
went for rain mixing with then changing to snow but accums are
forecast to be less than an inch.

The warmer GFS was eschewed for the cooler NAM, and Superblend temps
and dew points were lowered accordingly. NAM forecast soundings show
rain changing to snow from north to south during the night, with
snow expected to be the dominant precip type across the forecast
area by 12Z Thursday as low level cold advection and diurnal cooling
occurs overnight. Even so, thermal profiles are marginal as is the
saturation of the DGZ, so snow rates should not be heavy enough to
produce travel impacts.

This is a quick moving, progressive low which moves east and gets
absorbed into a larger scaler upper low across eastern Canada by
Thursday afternoon. So we expect the precip to wind down during the
morning and sfc ridging to build in with fair weather into early
next week.

&&

.AVIATION...(For the 06Z TAFS through 06Z Tuesday night)
Issued at 131 AM EDT Tue Apr 17 2018

Cyclonic flow in the wake of low pressure will continue to provide
primarily MVFR ceilings at West Michigan terminals through at
least the early morning hours. Flow across the lake and a weak
low-level boundary dropping southward through the area will
continue to provide scattered showers as well this morning,
lingering the longest at AZO, BTL, and JXN as north-northwest
winds focus activity more towards the I-94 corridor over the next
few hours. Some indications within a few hi-res model solutions
and upstream observations that ceilings could rise to VFR by
sunrise, but confidence is not high enough given flow off the
lake and will hold at high-end MVFR until trends begin to look
more apparent. Best potential for lower clouds to scatter out
looks to be after 00Z.

&&

.MARINE...
Issued at 320 PM EDT Mon Apr 16 2018

No changes to the marine headlines. Winds will gust to 30 knots
tonight before diminishing Tuesday. Waves will remain in the 5 to 10
foot range tonight before decreasing Tuesday.


&&

.HYDROLOGY...
Issued at 1138 AM EDT Mon Apr 16 2018

River levels are above normal in Southern Lower Michigan and around
normal in Central Lower Michigan. The significant precipitation over
the weekend has led to rising river levels across the area.
Continued rises are expected for the next several days. Minor
flooding near river banks is possible.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
LM...Small Craft Advisory until 8 PM EDT this evening for LMZ844>849.

&&

$$

UPDATE...MJS
SYNOPSIS...04
SHORT TERM...04
LONG TERM...Ostuno
AVIATION...HLO
HYDROLOGY...63
MARINE...04



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