National Weather Service Raw Text Product

Displaying AFOS PIL: AFDGRR Received: 2019-01-10 17:24 UTC


515 
FXUS63 KGRR 101724
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
1224 PM EST Thu Jan 10 2019

LATEST UPDATE...
Aviation

.SYNOPSIS...
Issued at 251 AM EST Thu Jan 10 2019

The following are the forecast highlights:

- Lake effect snow will diminish in coverage this morning with up
  to an inch of additional accumulation possible mainly along the
  lakeshore. Gusty northwesterly winds will also relax this 
  afternoon. 

- Wintry weather is looking less likely this weekend with areas along
  and south of I-94 having the best shot of up to 1" of snow.

- Warmer and relatively quiet weather is expected into early next 
  week. 

&&

.UPDATE...
Issued at 635 AM EST Thu Jan 10 2019

Based on the radar trends...the snow showers have been
diminishing. Guidance does suggest the clouds are becoming thinner
and are forecasted to do so through the day. Thus we lowered POPs
for today.

&&

.DISCUSSION...(Today through next Wednesday)
Issued at 251 AM EST Thu Jan 10 2019

A glimpse at regional satellite and radar loops (finally) reveals a 
scene typical of January with lake effect snow running like a well-
oiled machine across much of the Great Lakes. Moreover, temperatures 
are in the upper teens to lower 20s with gusty northwest winds of 15-
20 kts leading to wind chills in the upper single digits to lower 
teens.  All in all, it appears that winter has returned.

Despite a recent uptick in LES coverage this morning, a gradual 
downward trend is expected toward sunrise as winds veer northerly 
(shunting the bands of snow westward) and subsidence increases 
associated with a building ridge over the Great Lakes. Evidence of 
this trend can be seen in satellite imagery over Lake Superior as 
bands of lake-effect cloud cover are curving in response to the 
changing low-level winds and regional radar reflectivity factors
across all of Michigan have been decreasing in response to the 
lowering inversion heights. While the majority of the LES activity
will get pushed offshore this morning, light snow may continue 
sneaking into lake-bordering counties allowing for perhaps up to 
an additional half to one inch of fluff before snow ends by early
afternoon. Cloud cover make take some time to break across 
central Lower Michigan this morning and afternoon, but eventually 
at least broken cloud cover in tandem with decreasing winds should
allow for another chilly night with lows in the teens. (Note that
the average low for this time of year is in the upper teens... 
We've been spoiled so far this winter!)

After a relatively quiet Friday, attention will turn to the 
potential for wintry weather Saturday mainly along and south of I-
94. Forecast deterministic and ensemble model guidance is in 
excellent agreement that an upper-level shortwave trough will force 
the development of a low pressure system over the southern Plains 
Friday evening with a northeasterly track toward the Ohio River 
Valley on Saturday. Yet, the upper-level pattern will become 
somewhat benign as a secondary shortwave trough slides into the 
southwestern United States trapping a fairly stout surface high 
pressure system over the northern Great Lakes. Such a regime will 
effectively flatten the first trough and weaken upper-level support 
as the low slides northeast, all the while funneling dry air into 
the Lower Great Lakes. With this in mind, the deformation band may 
end up struggling to push into Lower Michigan with decreasing 
chances for precipitation with northward extent. Interestingly, 
forecast ensemble mean precipitation (and thus snowfall) from the 
ECMWF has actually increased over the past few runs for locations 
along I-94 with values anywhere from 0.1 to 0.15" translating to 1-
2" of snow. However, we would be surprised to see such totals given 
the aforementioned caveats, so we will feature slightly lower 
precipitation/snow totals with this forecast package; 1" or less 
mainly along and south of I-94.  

Sunday through Tuesday look relatively quiet with partly cloudy 
skies and highs in the low to mid 30s. Tuesday itself looks to be 
the warmest day in the forecast, with highs potentially approaching 
40. Cooler temperatures are then progged to make a return toward the 
middle of next week with perhaps additional chances for lake effect 
snow. 

&&

.AVIATION...(For the 18Z TAFS through 18Z Friday afternoon)
Issued at 1221 PM EST Thu Jan 10 2019

Latest vis loop shows some clearing over NE Lower and Saginaw 
Bay. It's trying to work westward but will take a while. So, we're
stuck with cigs around 2k ft through the afternoon. I'd expect 
the eastern TAF sites to become VFR first later this evening, 
followed by the rest of the sites overnight as some drier air 
works in to the region. 

&&

.MARINE...
Issued at 251 AM EST Thu Jan 10 2019

Winds and waves will relax this afternoon allowing for the 
expiration of the current Small Craft Advisory this evening. 
Relatively calm conditions are then expected through early next week 
thanks for light and off-shore winds. 


&&

.HYDROLOGY...
Issued at 330 PM EST Wed Jan 9 2019

Water levels are generally above normal for this time of year, but 
this will be changing this week with the return to winter 
temperatures. Precipitation will be in the form of snow, thus a 
trend toward dropping water levels is expected to take hold by the 
week's end across most of the rivers in West Michigan. Water 
temperatures are generally in the mid to upper 30s, except on the 
Muskegon River where lower 30s can be found. These values will 
fall through the weekend, and ice formation may be possible on 
rivers by next week. 

The Maple River at Maple Rapids continues to hover near bankfull, 
and is expected to remain around this level before a dropping trend 
starts by this weekend. No flooding is expected.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
LM...Small Craft Advisory until 7 PM EST this evening for LMZ844>849.

&&

$$

UPDATE...MJS
SYNOPSIS...Borchardt
DISCUSSION...Borchardt
AVIATION...04
HYDROLOGY...63
MARINE...Borchardt