109
FXUS63 KAPX 171727
AFDAPX

Area Forecast Discussion
National Weather Service Gaylord MI
127 PM EDT Sun Sep 17 2017

.UPDATE...
Issued at 1051 AM EDT Sun Sep 17 2017

Cold front just starting to push into Lake Michigan, on target to
slowly make its way east across our area this afternoon into early
evening. Mid level support becoming increasingly detached with time
as main shortwave trough rotates off well to the north. Lack of deep
layer forcing becoming increasingly evident as shower coverage along
the front continues to decrease, with what is left of much more
robust overnight showers now rotating into central upper Michigan.
With that said, area out ahead of the front has started to
destabilize, as evident by the recent development of high based
cumulus across northern lower. Temperatures expected to go up
several more degrees yet, supporting afternoon mean layer cape of
several hundred joules/kg. This should be enough to allow additional
convection to develop along the front, with the greatest development
expected across north central and northeast lower Michigan (very
possible areas of northwest lower see little shower activity). Not
expecting anything severe with limited mid level lapse rates and
only modest near surface instability. Still, any organized updrafts
will be capable of producing brief gusty winds through core precip
loading and wet microbursts. Overall flavor of inherited forecast
remains with just some minor refinement on cloud and expected shower
trends.

&&

.NEAR TERM...(Today through Tonight)
Issued at 324 AM EDT Sun Sep 17 2017

...Cold front to bring showers and t-storms today...

High impact weather potential...some t-storms, mainly this afternoon
and early evening.

Warm advection continues across northern MI, ahead of a mature
cyclone near the tip of the Keweenaw. Cold front making eastward
progress across western upper MI, central WI, and far eastern
Iowa. Clusters of deep convection (mostly in the form of non-svr
line segments) are ongoing along and ahead of the front. Some
initial, weak showers were in eastern upper MI earlier, but not
presently. The cold front will gradually cross northern MI from w
to e from midday thru early evening. Associated precip chances are
the main concern.

Cold front will go thru late enough to allow for diurnal heating/
destabilization ahead of it. This will mainly be the case in northern
lower MI (less cloud cover), and especially ne lower (later fropa).
But the primary shortwave is lifting into far northern Ontario today,
with only slow height falls here. That keeps temps aloft rather
warm, resulting in unimpressive lapse rates (5.6-6 C/km from 850mb
to 500mb). So, despite an unseasonably warm/moist BL (low/mid 80s
over low/mid 60s in spots), MlCape values will struggle mightily
just to approach 1k j/kg. In addition, best shear is well behind the
the front. in western upper MI/nw WI this afternoon. Our 0-6km bulk
shear values are only in the 10-20kt range. Maybe, just maybe, we
could a get a strong-ish wet microburst in ne lower MI this
afternoon, but the svr threat appears quite small. More likely are
just some locally heavy downpours.

That said, we have enough instability, forcing (front, some height
falls aloft), and moisture to support convection. Likely pops in
order in most of the forecast area, especially from 2 to 8 pm.
Perhaps just chancy pops w of US-131. Pops are needed a bit past
00z this evening in ne lower MI, but precip should be done by
midnight.

There is a lot of low clouds behind the front in Canada, though not
as much at our latitude. The latter is more relevant for us, given
the w to wnw post-frontal low level flow. But at least some stratocu
will roll into the area behind the front this evening into tonight.
That won`t be enough to keep some locales from decoupling and seeing
sharp temp falls tonight, especially for the cooler inland locales
in eastern upper MI. The above may also lead to some fog, especially
in places that get wet today.

Max temps from near 70f western Chip/Mack Cos to low/mid 80s ne
lower. Min temps mostly mid 40s to lower 50s.

&&

.SHORT TERM...(Monday through Tuesday)
Issued at 324 AM EDT Sun Sep 17 2017

...Low chances for scattered showers at various times...

High Impact Weather Potential: None.

Pattern Forecast: Sunday`s cold front and associated shortwave
embedded in broader troughing across the midsection of the country
continues to shift off to the east by Monday morning. High pressure
builds into the Great Lakes on Monday, followed by another shortwave
expected to race through the flow Monday night into Tuesday
morning...renewing low end chances across portions of northern
Michigan.

Primary Forecast Concerns/Challenges: More seasonable/normal
temperatures prevail Monday and Tuesday before warming back up
midweek; otherwise, pinpointing additional scattered shower chances
Monday night through Tuesday.

A significantly drier airmass will arrive behind Sunday`s departing
cold front, ultimately leading to a fairly pleasant Monday across
the area. Any lingering early morning fog is expected to gradually
dissipate coinciding with the diurnal cycle. Some additional patchy
fog will be possible Monday night, primarily across northeast Lower
where clouds will be fewer; however, increasing mid-high clouds over
the western half of the area should preclude much in the way of fog
development as you head toward Lake Michigan.

At this juncture, guidance continues to differ with respect to how
far north a moisture plume will extend Monday night into Tuesday in
conjunction with another perturbation aloft trekking across the
Great Lakes. As a result, lower than desired confidence prevails in
terms of shower chances for the second half of the forecast period.
The GFS progs an especially dry solution while the bulk of other
guidance remains in good enough agreement to warrant at least chance
PoPs (highest south of M-32) during the Monday night through Tuesday
morning timeframe. Certainly not a washout by any stretch of the
imagination and more so has the feel of nuisance/scattered showers.

Near normal high temperatures expected both Monday and Tuesday...
ranging from the mid-upper 60s north to the low-mid 70 south before
a more significant warm up is expected to prevail midweek through at
least next weekend.

.LONG TERM...(Tuesday night through Saturday)
Issued at 324 AM EDT Sun Sep 17 2017

High impact weather potential: Minimal.

High amplitude ridging is progged to build across the midsection of
the country with the main story revolving around high temperatures
once again climbing back above normal. It`s not out of the realm of
possibilities that some locations flirt with record high temps by
next weekend. Occasional showery periods may present themselves at
various times throughout the period with the best threat looking to
be during the Wednesday night - Thursday timeframe, although some
guidance is already hinting at a line of showers off to our west
decaying significantly on their approach to northern Michigan.

&&

.AVIATION...(For the 18Z TAFS through 18Z Monday afternoon)
Issued at 125 PM EDT Sun Sep 17 2017

Cold front will cross west to east across the area this afternoon
and early evening. Showers, and perhaps a few thunderstorms, will
develop along this front, with the greatest coverage expected
along and east of Interstate 75. May see brief periods of MVFR
cigs as these showers pass overhead. Band of MVFR cigs expected to
develop in the post-frontal environment for a few hours this
evening, with cigs likely lifting and scattering out through the
overnight. More high clouds expected Monday morning. Southwest
winds expected to become northwest to north after the cold front
passes.

&&

.MARINE...
Issued at 324 AM EDT Sun Sep 17 2017

Cold front will cross northern MI from w to e this afternoon/early
evening. Southerly winds will veer west just behind the front this
afternoon, and become lighter from the north tonight. Advisories
should not be necessary.


&&

.APX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
LH...NONE.
LM...NONE.
LS...NONE.
&&

$$

UPDATE...MB
NEAR TERM...JZ
SHORT TERM...MG
LONG TERM...MG
AVIATION...MB
MARINE...JZ