Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 131123
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
623 AM EST Mon Feb 13 2017

LATEST UPDATE...
Aviation

.SYNOPSIS...
Issued at 325 AM EST Mon Feb 13 2017

Today should see considerable sunshine and unseasonably mild
temperatures as a large Pacific origin high pressure system
passes south of the state. Tonight a system from the Canadian
arctic heads nearly due south, while the center of the surface low
passes north of Michigan we get into the flow around it so that
will mean mild temperatures will continue through most of Tuesday
before cold front from the system passes through the area
Wednesday night. That brings the cold air and lake effect snow
showers back to the area into Thursday morning. A series of
Pacific storms track north of Michigan into early next week. That
puts this area in the warm air this coming weekend into a least
early next week. We could see highs in the 60s at some point this
coming weekend or early next week.

&&

.SHORT TERM...(Today through Wednesday)
Issued at 325 AM EST Mon Feb 13 2017

My forecast issue tonight is the snow shower activity for Tuesday
night into Wednesday. The issue there is just how strong to play
it in the wording of the forecast.

Somewhat like last Wed and Thursday we have another one of those
shallow cold fronts that comes through the area Tuesday evening.
The polar jet does go south of us and over the years (to many to
count) I have noted if the polar jet is not south of this area the
inversion heights are to shallow no matter how cold the air is and
there is very little or no snow showers. In this case through the
polar jet gets south of the state by early Wednesday morning and
does not pass east of us again till Thursday morning. Of course
one needs a near saturated layer in the DGZ to get snow from a set
up like this and in this case we do have that. This is not
totally different than last week (Wed and Thu) when we had this
sort of set up and even through inversion heights were around 4000
ft we got snow showers the entire time we were on the cyclonic
side of the polar jet.

Now in this case the GFS has higher inversion heights than the NAM
does (not typically what we see). Even so both show inversion
heights mostly under 6000 ft so what we will get will be limited.
Still it will snow even so. There is lift and the DGZ, the surface
air temperatures will be in the 20s during the day Wednesday (for
the most part) so that is more than cold enough to get lake effect
snow going. Also the CIPS analogs show 2 to 4 inches west of
US-131 for this event. I will admit 6 out of 15 show no snow but
that means 9 out of 15 do. So, I am going with this idea and I
increased the pop to 60 pct Wednesday. No big snows, mostly a
around an inch will fall but it will be snowing. Inland of US-131
with a north northwest wind in the boundary layer, it will just be
seasonably cold with little or no snow showers.

.LONG TERM...(Wednesday night through Sunday)
Issued at 325 AM EST Mon Feb 13 2017

Lake effect snow showers may linger into Thursday morning along the
lakeshore. The remainder of the period is dominated by dry
conditions and moderating temperatures.

An upper level low will be situated well to the east over portions
of New England by Wednesday night. That leaves us well behind the
system in north-northwest flow with the upper jet just south of
Lower Michigan. Though lake effect snow showers will be possible
into early Thursday morning, a shallow and gradually thinning DGZ
will continue to point toward decreasing activity. As we progress
through Thursday morning, we get onto the anticyclonic side of the
stream, bringing an end to the lake effect setup.

A warm front pushes through the area Thursday afternoon and evening.
The DGZ is elevated above 10k feet and while RH values are nearing
90 percent overhead in some locations, lift is rather weak. Even
when moisture is best, there is a 100-150mb dry layer down low,
leading me to believe that much of what falls will evaporate before
hitting the ground. While a flurry or brief light snow shower isn`t
impossible, trends are not in its favor with dry weather more likely.

Southerly flow kicks in for the later part of the week and really
takes over for the weekend. Upper ridging begins to influence Lower
Michigan as surface high pressure settles over the Great Lakes.
Plenty of dry air could lead to sunshine as early as Friday morning.
This could extend right through the weekend. Ensembles generally
land somewhere in the 50s, but hint at pushing 60 in some cases. It
will be something to keep an eye as model guidance sometimes tends
to over amplify the ridge several days out. Regardless, it looks
like it is shaping up to be a spectacular weekend if all holds.

$$

&&

.AVIATION...(For the 12Z TAFS through 12Z Tuesday morning)
Issued at 623 AM EST Mon Feb 13 2017

High pressure passing just to the south of Michigan today will
result in nearly clear skies through the day. High clouds will
move in this evening and so will Low Level Wind Shear as winds
will increase to over 40 knots just 2000 ft above the ground while
surface winds are south southwest around 10 knots.

&&

.MARINE...
Issued at 342 AM EST Mon Feb 13 2017

The small craft advisory has been extended into Wednesday morning.


&&

.HYDROLOGY...
Issued at 302 PM EST Sun Feb 12 2017

River levels continue above normal and minor flooding continues on
the Grand River at Ionia. Little precipitation is expected through
the week and temperatures will be above normal, so river levels
should fall into next weekend.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
LM...Small Craft Advisory until 7 AM EST Wednesday for LMZ844>849.

&&

$$

SYNOPSIS...WDM
SHORT TERM...WDM
LONG TERM...JAM
AVIATION...WDM
HYDROLOGY...63
MARINE...WDM



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