National Weather Service Raw Text Product

698 
FXUS63 KAPX 201104
AFDAPX

Area Forecast Discussion
National Weather Service Gaylord MI
604 AM EST Tue Nov 20 2018

.NEAR TERM...(Today through Tonight)
Issued at 335 AM EST Tue Nov 20 2018

High impact weather potential: More accumulating snow and 
possible blowing snow for some areas. 

Pattern synopsis and forecast:

Upper level troughing and associated forcing, sfc low and deeper 
moisture are all exiting east early this morning. Much colder, but 
quite dry air was working into the region via some gusty northerly 
winds that have been developing. This is out ahead of sfc high 
pressure which extended from the Plains to Ontario. This colder air 
was producing some weak lake effect in north low level wind flow 
regimes. Certainly nothing that is too impactful. Upstream across 
central Canada, we already see the next shortwave and it's 
associated sfc low which was working into Manitoba. This system was 
taking a continental track and appears to not have a ton of moisture 
with it based on some current Canadian obs. 

Scattered weak lake effect snow showers in northerly flow regimes 
will slowly translate northward through the day as 1000-850mb winds 
gradually back to out of the WSW by later this afternoon. This is 
due to the high pressure drifting across nrn Michigan and the 
approach of the aforementioned Canadian shortwave. Snow accumulation 
will be fairly minor due to the shifting winds and relative dryness 
of the BL. That said, there will be some late day enhancement, as 
the "deeper" moisture, WAA, DPVA and light snows from this system 
arrive, starting the better seeder-feeder process. The better 
snowfall is expected to be this evening though, and it's really a 
quick-hitting kind of deal. However, the UVV's are quite impressive, 
and there is a rather deep and near isothermal DGZ. Max lift however 
is just under this dendritic growth zone based on many data sets. 
Another similar looking scenario overnight, like the one ongoing 
now. Much colder air filters into the region with H8 temps falling 
to as -14C south to -20C north, and even with the large delta t's 
and inversion heights to 5-6kft, the moisture in the BL is expected 
to be relatively shallow, with and inverted V layer up to 3kft. 1000-
850mb flow will be veering all night too. Swinging from WSW to NW, 
spreading out snow showers across a larger area.  

Snowfall totals will be greatest across NW lower over to Drummond 
Island, as the best snows occur while low level winds are out of the 
WSW. Generally 1-2" totals there, but 2-4" north of M-32 and west of 
I-75. An inch or less most other areas, down to none expected in NE 
lower, in the far SE CWA toward Saginaw Bay. 

Current gusty winds will be weakening through first half of the day 
as high pressure arrives. The gradient tightens back up rather 
quickly later this afternoon and through the night, as the sfc low 
pressure tracks north of us and we stay in the tight gradient 
through the night. Gusts of 20-25mph are possible by early evening, 
and a mixed BL will keep similar numbers going through the night. 
Areas along the NW lower and Whitefish Bay coasts are likely to feel 
some 30-35mph gusts tonight. Blowing snow expected at times this 
evening.

Highs today quite chilly, in the mid to upper 20s most areas. Lows 
tonight ranging from 10-15F in eastern upper to 15-20F in most of 
nrn lower outside of the NW flow regimes where clouds look to hold 
readings in the lower half of the 20s. 

&&

.SHORT TERM...(Wednesday through Thursday)
Issued at 335 AM EST Tue Nov 20 2018

...Cold but mostly quiet for Thanksgiving...

High Impact Weather Potential...Minimal aside from wind chills in the 
single digits below zero Wednesday night.

Pattern Synopsis/Forecast...Troughing will deepen over eastern 
Canada and the Northeast on Wednesday as a ~130 knot upper jet 
streak digs into the Great Lakes region. At the surface, a departing 
clipper system will be displaced by a strong Canadian surface high (+2 
standard deviations above the mean) and a surge of colder air sliding 
into the Upper Great Lakes for Thanksgiving. The high will slide off to 
our east by Thursday afternoon, giving way to increasing warm air 
advection and rising heights over northern Michigan as mid-level 
ridging approaches.

Primary Forecast Concerns...Transient small lake effect snow chances 
and Wednesday night low temperatures.

Tight thermal and pressure gradients over northern Michigan will lead 
to strong cold air advection on Wednesday as we sit between the 
departing clipper system and the encroaching strong Canadian high. H8 
temperatures will quickly drop in the morning, ranging from -16C over 
our southwestern counties to -21C over eastern Upper through evening. 
This will, of course, promote favorable over-lake instability, but 
moisture looks to become pretty limited as PWATs drop to ~0.1" or less 
over eastern Upper and northeast Lower. Forecast soundings tell a 
similar story, with low level moisture and inversion heights only 
up to 5 to 6 kft and perhaps some dryness to overcome just off the 
surface. Certainly not anticipating any significant activity given 
limited moisture, but perhaps locally up to an inch Wednesday morning 
within heaviest snow bands in NNW flow snowbelts. Shouldn't have 
too much impact on holiday travel across northern Michigan. Activity 
should mostly dissipate Wednesday evening as low level winds shift to 
the NNE and subsidence increases aloft beneath the building high. 
However, there may be a lingering band that pushes out over central 
Lake Michigan and another over Lake Huron that likely won't pose any 
impact to land.

Other big focus will be cold temperatures through Thanksgiving morning 
as the brisk northerly winds on Wednesday usher in an unseasonably cold 
airmass. Highs Wednesday will range from the teens across eastern Upper 
to the 20s across northern Lower (near 20 degrees north of M-32). 
925/850mb temperatures over northern Michigan are then progged to 
drop to 2 standard deviations below the mean for this time of year by 
evening. Skies are expected to at least partially clear across much of 
the area Wednesday evening (especially along the I-75 corridor) before 
mid-level clouds begin to increase somewhat during the second half of 
the night. Winds will become light as the high slides overhead, but the 
boundary layer likely won't become completely decoupled as per forecast 
soundings. Still expect an efficient radiational cooling setup, which 
will only be aided by current snowpack. Trended closer to MOS guidance 
for Wednesday night's lows, with single digits across most of the area, 
coldest across eastern Upper and interior northern Lower where lows are 
expected to be closer to 0 degrees. 

Partly sunny skies and generally quiet weather in store for 
Thanksgiving day. Still on the cold side, but most areas at least a few 
degrees warmer than Wednesday. Very small chance for perhaps some 
flurries coming ashore north of Saginaw Bay during the afternoon as 
veering winds become SSE. 

.LONG TERM...(Thursday night through Monday)
Issued at 335 AM EST Tue Nov 20 2018

High Impact Weather Potential...Minimal.

High pressure pushes off to the east Thursday night with southerly 
return flow drawing increasing moisture into the region through 
Saturday morning. Mid level ridge axis will cross northern Michigan 
Friday morning, leading to more moderate temperatures through the 
weekend. A deep trough and associated cold front are then progged to 
interact with the increasingly moist airmass to bring widespread 
precipitation late Friday night into Saturday, mostly in the form of 
snow Friday night before transitioning to rain Saturday morning. 
Another system developing over the Plains will eject towards the Lower 
Great Lakes later in the weekend, bringing more precipitation chances 
to northern Michigan Sunday and Monday. Colder conditions make a return 
on the backside of this system heading into the middle of next week.

&&

.AVIATION...(For the 12Z TAFS through 12Z Wednesday morning)
Issued at 604 AM EST Tue Nov 20 2018

High pressure will cross nrn Michigan today, before low pressure arrives
tonight north of the region. Current gusty northerly winds will 
weaken through the first half of today, while also backing more 
out of the WSW by late this afternoon, while also increasing as 
the pressure gradient tightens in advance of the low pressure. The
gradient remains tight through the night, and gusty winds veer 
back to out of the NW behind the passage of a cold front. 

Out ahead of the low pressure, light snows will break out late
this afternoon and through mainly this evening, enhancing ongoing
light lake effect. This will lead to around an inch at TVC/MBL,
minimal at APN, but maybe up to 3 inches at PLN. MVFR Snow ratios
will be around 18:1 with snowfall rates under an inch per hour.
These better snows exit later tonight with just some very minor
lake effect with minimal VSBY restrictions (MVFR). 

&&

.MARINE...
Issued at 335 AM EST Tue Nov 20 2018

Winds will continue to wind down into daybreak with sub advisory 
speeds expected for at least the first half of today as high 
pressure crosses the region. Low pressure will be passing to the 
north tonight and the pressure gradient tightens rather quickly 
later today. We stay in that tight gradient through tonight and into 
Wednesday. Advisory level winds start developing by early this 
evening in the nearshores of nrn Lake Michigan, then spread 
throughout all areas tonight and continue into Wednesday. Gale force 
gusts are anticipated in coastal convergence areas from the Bridge 
down through Presque Isle Light. Will continue to ride the gale 
watch since this doesn't start until late tonight into Wednesday 
morning. High pressure and lighter winds arrive Wednesday afternoon 
into Wednesday night.


&&

.APX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
LH...SMALL CRAFT ADVISORY until 5 PM EST Wednesday for LHZ345-346.
     SMALL CRAFT ADVISORY until 5 AM EST Thursday for LHZ349.
     GALE WARNING from midnight tonight to noon EST Wednesday for 
     LHZ347-348.
LM...SMALL CRAFT ADVISORY until 5 PM EST Wednesday for LMZ323-341-342-
     344>346.
LS...SMALL CRAFT ADVISORY from 7 PM this evening to 5 PM EST 
     Wednesday for LSZ322.
     SMALL CRAFT ADVISORY until 5 PM EST Wednesday for LSZ321.
&&

$$

NEAR TERM...SMD
SHORT TERM...MK
LONG TERM...MK
AVIATION...SMD
MARINE...SMD