Area Forecast Discussion
Issued by NWS Gaylord, MI

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FXUS63 KAPX 230520

Area Forecast Discussion
National Weather Service Gaylord MI
120 AM EDT Fri Oct 23 2020

Issued at 900 PM EDT Thu Oct 22 2020

Elongated low pressure center has reached Iowa late this evening.
Associated warm front is draped across Southern Lower Michigan.
Long corridor of convection continues to fire north of this warm
front...impacting areas from the Central Plains thru Iowa and
Wisconsin into Northern Michigan. Broad area of snow continues to
develop north of this convective corridor. Upper level jet max is
providing good upper support for all of this precip production...
along with deep moisture. Convection is also being driven by
MUCAPES of 1000-1500 J/kg...although convection is largely
elevated within our area.

Low center will continue to track NE into Lower Michigan
overnight. Widespread showers and embedded thunderstorms will
continue to fire across our CWA...with the greatest chances of
precip across the NW two-thirds of our CWA along and northwest of
the surface low track. Do not anticipate any severe storms with
the expectation of convection remaining elevated in nature. Heavy
rainfall will remain possible...and will continue to watch precip
estimates overnight.

Temps will actually warm a bit overnight as low level WAA
continues ahead of the low center. By daybreak...temps will range
from the upper 30s to around 40 in Eastern Upper Michigan to
around 60 degrees near Saginaw Bay.


.NEAR TERM...(Through Friday)
Issued at 405 PM EDT Thu Oct 22 2020

...Rain, at times heavy, through Friday...

High impact weather potential: Locally heavy rain leading to ponding
of water in poor drainage areas. A few non-severe thunderstorms.

Pattern synopsis/forecast:

Rapidly tightening thermal gradient found across the western Great
Lakes early this afternoon as deep and moist warm air advection
spreads north ahead of approaching northern Plains shortwave trough.
Weak surface low developing across southwest Iowa/northwest
Missouri, with its attendant warm front stretching northeast across
southern lower Michigan. Intense right entrance region upper jet
dynamics enticing quite the low level jet response, with 50+ knot H8
level jet punching northeast into central Wisconsin. Forced
mass/moisture convergence on the nose of this low level jet and
growing frontogenetical response...both overtopped by that bullseye
of upper level divergence, helping drive an expanding area of
showers with embedded thunderstorms into the western Great
Lakes...including much of northern Michigan.

Core of upper level divergence slowly slides east tonight, with
focused fgen response doing the same. Weak low pressure pivots
northeast along this tightening baroclinic axis, cutting across our
area during the early morning hours. Combination of all the above
within impressive deep layer moisture surge is setting the stage for
a rather wet period of weather over the next 24 hours.

Primary forecast concerns/challenges: Addressing rainfall totals and
potential flooding concerns.


Expect shower coverage to only increase with time the remainder of
this afternoon into tonight as earlier mentioned forcing spreads
overhead. Fgen response, while narrow, will be impressive, with warm
side enhanced lift working on a moisture rich airmass featuring
precipitable water values exceeding 1.25 inches (over 2 standard
deviations above normal for this time of year). Corridor of elevated
cape within the primary fgen response will only aid in updraft
potential. Expect rain to come down heavy at times this evening into
the early overnight when juxtaposition of all the above is
maximized. Addressing the corridor of heavier rain remains a more
formidable forecast challenge. Recent guidance trends, supported by
real-time observations, has displaced the axis of heaviest rains a
bit further north than earlier anticipated, cutting across the Tip
of the Mitt into eastern upper Michigan. Could easily see rain
totals in excess of 1.50 inches in this corridor, with localized
amounts over 2 inches where thunderstorms occur. Not enough to pull
the trigger on any type of flood headlines, but definitely could see
some ponding on roadways and in areas of poor drainage (with the
latter exacerbated by ongoing leaf fall). Expect rain amounts to
steadily decline the further south one goes, with areas down near
Saginaw Bay likely seeing little rainfall overnight after passage of
surface warm front.

Low pressure passes quickly off to our east early Friday, dragging
its attendant cold front west to east across the northern Lakes.
Upper and mid level support will be much slower to depart with mid
level impulse and those upper level jet dynamics spreading overhead.
These will continue to activate trailing elevated front, keeping
fairly widespread showers across much of the area, especially through
the early afternoon hours. While heaviest rains will have departed,
could easily see some places receive another half inch or so,
especially where some elevated thunderstorms occur.

As for temperatures, a definite non-diurnal curve expected through
the near term...with temperatures increasing tonight into early
Friday (hitting the 60s across our southeast counties), with
readings steadily dropping as we head through Friday.


.SHORT TERM...(Friday night through Sunday)
Issued at 405 PM EDT Thu Oct 22 2020

...Chilly with Lake Effect then Rain/Snow...

High impact weather potential: Low.

Primary forecast concerns/challenges: Pops and precipitation type.

Colder air will continue to advect into the region Friday night and
hold across the region through the period. It will be plenty cold
enough for lake effect precipitation with lake/850 mb delta ts of
around 20. However, there are a few factors to take into account on
the negative side. Surface high pressure and associated drier air
build in from the west late Friday night into Saturday. North
northwest winds back into the northwest but decrease to under 10
knots by early Saturday. So do expect at least scattered
precipitation in the form of rain near the lakeshores and snow
farther inland Friday night (with perhaps a thin coating of snow in
a few areas) which should trend down to isolated coverage Saturday
due to the lighter wind regime. Perhaps a few leftover isolated rain
or snow showers Saturday night. A decent short wave moving through
the flow is then expected to bring widespread precipitation to the
region on Sunday, especially in the afternoon. Looking at model
soundings, it`s looking like mainly snow in the higher terrain of
northern lower and inland areas of eastern upper with rain near the
lakeshores. Therefore, will trend the forecast in this direction. Am
not expecting much in the way of accumulation Sunday as temperatures
should remain above freezing. Temperatures will be several degrees
below normal (especially during the day). Forecast lows are in the
mid 20s to mid 30s and highs in the upper 30s to mid 40s.

.LONG TERM...(Sunday night through Thursday)
Issued at 405 PM EDT Thu Oct 22 2020

High Impact Weather Potential: Minimal. P-type issues at times.

Cool and unsettled weather pattern looks to set up across the Great
Lakes for the first half of next week...leading to below normal
temps and potential for p-type issues at times. Strong mid to upper
level ridging in the Gulf of Alaska hangs out through the
period...allowing for troughing to set up across the west central
US. A bit of a split flow looks to ensue over the US...with a closed
low developing over the western US and slowly meandering eastward
through the period. In the meantime...a few shortwaves speeding
through the northern portion of the flow could give us a few shots
at precipitation chances...and reinforce the cooler air over the
region...especially as troughing slowly moves to the east.
Uncertainty in the evolution of the aforementioned closed low will
lead to uncertainty in downstream effects over the Great Lakes going
into midweek next week.


.AVIATION...(For the 06Z TAFS through 06Z Friday night)
Issued at 120 AM EDT Fri Oct 23 2020

A tight pressure gradient with LLWS will briefly loosen up as low
pressure crosses nrn Michigan through Friday morning. Wind
directions will be highly variable as this low crosses the region.
The pressure gradient tightens back up through Friday behind this
low pressure and it`s associated strong cold front, and winds will
shift sharply out of the NW and become quite gusty. The cold
advection will bring some scattered lighter lake effect rain showers
this evening, which will gradually mix with, or changeover to snow
through tonight and Saturday. Higher pressure moves in late Friday
night into Saturday, which will allow winds to subside.

CIGS will largely be LIFR through most of Friday, in continued
moderate to heavy rainfall that will gradually shift over into NE
lower/APN, before strong cold advection brings improving CIGS to MVFR
Friday evening, and high end MVFR/low end VFR late Friday night.


Issued at 405 PM EDT Thu Oct 22 2020

Period of gusty winds across the Great Lakes tonight and Friday as
low pressure slides up and across the area. Strongest winds will be
on Friday as post-system cold air advection develops in northwest
flow regime. Widespread small craft conditions likely, with even the
threat for a few isolated gales on northern Lake Michigan and along
the northeast lower coastline Friday. Winds steadily subside Friday
night on into the start of the weekend. Widespread showers with a
few embedded thunderstorms expected tonight into Friday. Sharply
cooler weather for the weekend.


MI...FLOOD WATCH through this afternoon for MIZ016>018-020>022-025-
LH...SMALL CRAFT ADVISORY until 11 PM EDT this evening for LHZ345-346-
     GALE WARNING from 6 PM to 11 PM EDT this evening for LHZ347-348.
LM...SMALL CRAFT ADVISORY until 11 PM EDT this evening for LMZ341.
     GALE WARNING from 2 PM this afternoon to 11 PM EDT this evening
     for LMZ323-342-344>346.
LS...SMALL CRAFT ADVISORY until 11 PM EDT this evening for LSZ322.
     GALE WARNING from 2 PM this afternoon to 11 PM EDT this evening
     for LSZ321.


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