Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 231732
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
132 PM EDT Mon Apr 23 2018

LATEST UPDATE...
Aviation

.SYNOPSIS...
Issued at 330 AM EDT Mon Apr 23 2018

High pressure will provide another mostly sunny and mild day with
high temperatures near 70. A slow moving low pressure system
tracking south of Michigan will bring clouds and scattered light
rain showers for Tuesday. After today, cooler temperatures,
generally in the 50s, will prevail through the rest of the week.

&&

.SHORT TERM...(Today through Wednesday)
Issued at 330 AM EDT Mon Apr 23 2018

No significant changes to the fcst. While some high level
cloudiness will move in from the south today, it should be thin
enough to allow for highs close to 70. Thicker clouds arrive
tonight, with chance pops for light rain arriving late mainly
along and south of I-96. Initial band of showers will probably
get mostly chewed up by our dry air mass, with better risk of
showers on Tuesday once better saturation occurs.

The other player on Tuesday/Tuesday night in addition to the
upper low over the Ohio Valley is a nrn stream trough and cold
front approaching from the northwest. Models are hinting at
better probability of showers developing later Tuesday across
central and northern Lower Michigan ahead of this feature. This
area should receive more insolation than srn Lwr MI, so a diurnal
component combined with wk sfc convergence and the apchg wave
should result in scattered afternoon and evening convection. Not
forecasting thunder up north at this time, although models do show
a few hundred joules of MUCape developing at pk heating.

Confidence is low regarding departure of the rain threat as new
00Z ECMWF wants to hold onto a shower threat into Wednesday -
especially east of hwy 131. For now will keep Wednesday dry with
decreasing clouds, but may need to add pops in ern sections in
later fcsts.

.LONG TERM...(Wednesday night through Sunday)
Issued at 330 AM EDT Mon Apr 23 2018

A ridge of high pressure will bring fair weather with seasonable
temperatures Wednesday night through Thursday. We did notice that
the 00Z ECMWF now suggests that clouds and even some rain/snow
showers may develop/linger Wednesday night. However this latest
ECMWF run is an outlier among latest medium range guidance
solutions. Therefore we maintained the dry fcst Wednesday night but
will continue to monitor medium range guidance trends.

A low pressure system will move in from the west and bring a chance
of showers late Thursday night and Friday. It is not completely
impossible that some wet snow flakes may mix in with pcpn early
Friday over our northern fcst area.

However this is not the most likely outcome and we continued to
favor the ECMWF solution in which case p-type will be plain rain.
Sfc temps even across our northernmost fcst area should stay
above freezing so no winter wx type impacts are expected even if a
few wet snow flakes were to mix in.

A cooler airmass will briefly advect in behind that system Friday
through Saturday when high temperatures will only reach the lower to
perhaps middle 50`s. Temperatures will then undergo a slow
moderating trend late in the weekend into early next week as the
colder air retreats back northward.

&&

.AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon)
Issued at 127 PM EDT Mon Apr 23 2018

As the low pressure system nears from the south...this will cause
the clouds to thicken up and lower. This will take some time
though...as the airmass is currently very dry. Thus this evening
and more so tonight...we will feature MVFR conditions arriving
from the south...and eventually some showers. Current the computer
models are showing widespread IFR/LIFR developing late tonight
into Tuesday morning. Given the dry conditions near the surface
right now...I did not go quite that low. Will need to monitor
trends.

&&

.MARINE...
Issued at 330 AM EDT Mon Apr 23 2018

Winds and waves remaining below small craft advisory criteria
through Tuesday, then northerly flow ramping up Tuesday night into
Wednesday could necessitate marine headlines.


&&

.FIRE WEATHER...
Issued at 330 AM EDT Mon Apr 23 2018

Will have another day of elevated fire danger today as
temperatures approach 70 with RH values dropping into the 20s
this afternoon. Winds may gust at times to 20 mph during pk
heating when deeper mixing is present.

&&

.HYDROLOGY...
Issued at 309 PM EDT Sun Apr 22 2018

Lowland nuisance flooding near some riverbanks will be ongoing
over the next few days as water from last weekend`s mixed
precipitation event moves through the river basins. Since no heavy
rain events are anticipated in the next week, rivers will
gradually subside.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
LM...None.
&&

$$

SYNOPSIS...Meade
SHORT TERM...Meade
LONG TERM...Laurens
AVIATION...MJS
FIRE WEATHER...Meade
HYDROLOGY...CAS
MARINE...Meade


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