Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 141128
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
628 AM EST Wed Feb 14 2018

LATEST UPDATE...
Aviation

.SYNOPSIS...
Issued at 328 AM EST Wed Feb 14 2018

High pressure will bring fair weather today. Low pressure will
track south of Lower Michigan on Thursday with rain changing to
snow by Friday.

&&

.SHORT TERM...(Today through Friday)
Issued at 328 AM EST Wed Feb 14 2018

Primary forecast issue in the near term is for transition of precip
type from rain to snow Thursday night as colder air filters back
in. For today...low level moisture advects in on southwest flow
late this afternoon and evening. Forecast soundings continue to
show the moisture is shallow with the DGZ unsaturated...so only
drizzle or light rain is expected.

The northern and southern streams remain separate through
Thursday with Lower Michigan on the northern periphery of the
precip shield of a sfc low tracking across the Ohio Valley. Bulk
of the rain looks to remain south of the Michigan border and
light rain showers across the forecast area, with a change to snow
beginning by evening across the northern tier and working south to
the southern tier by Friday morning. Only light accums expected
through Friday including a period of northwest flow lake effect
snow showers into the afternoon.

.LONG TERM...(Friday night through Tuesday)
Issued at 328 AM EST Wed Feb 14 2018

A colder period still looks good for the weekend, in fact the models
have backed off on the warm up by about a day, so Sunday also looks
chilly now.  This occurs as yet another cold front cuts across the
CWA Saturday evening.  The system should give us another quick shot
of snow too, with accums under an inch.

Quite a few model differences arise from Sunday through Tuesday,
leading to low forecast confidence.  A warm up should occur, but the
models are in disagreement as to it`s timing and magnitude.  Weak
upper ridging should signify the beginning of the warming trend by
Sunday night.  The ECMWF is much more aggressive with the surge of
warm air, where the GFS is slower moving the surface high pressure
to our east, so the Gulf moisture and warmth is delayed.  In this
regime it makes sense to have the potential for a light wintry mix
across the northern CWA in the stronger region of warm advection.

Then a wetter system should move in by Monday lasting into Tuesday.
A slow moving surface boundary with several waves of weak low
pressure along it will bring this pcpn.  The models continue to
struggle with the low level temp regime and whether we completely
scour out the cold air.  However the ECMWF readily does do this,
pointing toward mostly rain.  Enough doubt in how this unfolds
however, and the movement and timing of the front, so will have the
mention of freezing rain and rain.

&&

.AVIATION...(For the 12Z TAFS through 12Z Thursday morning)
Issued at 628 AM EST Wed Feb 14 2018

MVFR conditions today as haze and light fog persist much of the
day. Then IFR expected to develop overnight as low level moisture
continues to increase, forming low stratus and fog. Winds will be
southwest around 10 knots.

&&

.HYDROLOGY...
Issued at 1101 AM EST Tue Feb 13 2018

A warm up this week and up to a quarter inch of rain Thursday should
result in melting snow and ice, and rising river levels. This could
also result in shifting ice and additional ice jam formation.

A flood advisory remains in effect for the Looking Glass River near
Eagle due to elevated levels of water/ice from an ice jam. River
levels in the vicinity of ice jams will continue to fluctuate by
several feet until the ice breaks free.

&&

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

$$

SYNOPSIS...Ostuno
SHORT TERM...Ostuno
LONG TERM...JK
AVIATION...Ostuno
HYDROLOGY...63



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