Area Forecast Discussion
Issued by NWS Gaylord, MI

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787
FXUS63 KAPX 231427
AFDAPX

Area Forecast Discussion
National Weather Service Gaylord MI
1027 AM EDT Mon Oct 23 2017

.UPDATE...
Issued at 1026 AM EDT Mon Oct 23 2017

Very dynamic system just starting to come together in the region.
Southern stream system is lifting into central IN, while northern
stream energy digs toward northern MN. These systems will phase
and result in explosive cyclogenesis, which is kicking into gear
right about now.

Of course, we`ve already had 1-1.5 inches of rain, from a system
that is only `just starting to come together`. Rain continues in
most areas, but is only spotty from APN to Tawas, and tapers to
nothing near and west of I-75 in eastern upper MI. Rainfall
intensity is in something of a lull, though we will swing back the
other way this afternoon. We appear to remain on track for a
general 2-5 inch rainfall thru Wed, with the heaviest amounts this
afternoon and tonight. In fact, this system is an overachiever to
this point, and wonder if the above forecast rainfall totals
could be a little low.

So, will this cause problems? Widespread problems? It`s difficult
to come up with an analog event: this much widespread rain, not
associated with an MCS or even convection (we`re not outlooked
for thunder by SPC), and therefore being a somewhat drawn-out
event. We are not flood-prone here, given our sandy soils and
generally rural demographics; these factors are even more
prominent in a longer-duration event. We have a lot more clay-
based soils in the far se, and they are much more flood-prone as
result - but that area now looks to have less rain than most.
Regarding soil moisture, our short-term memory is dry weather for
a solid week until yesterday; our long-term memory is of a wet
year or two.

Will be maintaining the flood watch. Some thought being given to
a pre-emptive flood warning in parts of northern lower MI, but
don`t wish to go down that road yet. Will add eastern upper to the
watch, with the emphasis near and east of I-75; there are some
flood-prone locales (Rudyard/Kinross) that have gotten and will
get additional heavy rain.

This system will also pose considerable challenges re: winds, with
explosive cyclogenesis that proceeds to wrap back right over our
heads. Strongish winds could develop in some well-exposed locales
as soon as midnight tonight. By dawn Tuesday, eastern upper MI
will have relatively little wind (directly beneath the low), while
the nw lower MI coast will be quite blustery.

More to come later today. The ongoing forecast adequately covers
the ongoing and expected wx today, and other than some fine-
tuning, no major changes (other than flood watch expansion) are
planned at this time.

&&

.NEAR TERM...(Today through Tonight)
Issued at 347 AM EDT Mon Oct 23 2017

...Stretch of wet weather ahead...

High Impact Weather Potential...heavy rainfall/flooding potential
across northern lower Michigan.

Pattern Synopsis/Forecast...Broad high falls continue to spread into
the northern plains facilitated by a strong pacific jet and associated
short wave energy digging into the Dakotas this morning. Southern
piece of short wave energy has largely pinched off from the main
upper trough (temporarily) and migrating through the lower-middle
Mississippi River valley. At the surface...slowing cold front has
finally pressed eastward into Lake Huron and stretches down through
Saginaw Bay into southern lower MI...continuing to another surface
wave over western Kentucky. However...a nicely defined deformation
axis and a narrow moisture rich corridor (PWAT values in excess
of 1.5 inches) stretches from the Missouri up through northern
lower Michigan...where persistent post-frontal rainfall continues
this morning.

Primary forecast concerns...hydro.

Southern piece of short wave energy and (attending deepening
surface low) still looking to open up and accelerate northeastward
into the Ohio Valley today and up through the Great Lakes
tonight...in response to strong pacific jet energy digging into
the central/southern plains. Strong deformation and upper jet
forcing acting on the aformentioned moisture plume continues to
set the stage for a prolonged heavier rainfall event up through
lower Michigan...especially this afternoon through tonight.
Increasing model consensus pegs that corridor of persistent heavy
rainfall from SW lower Michigan right up through northern lower
Michigan. Total rainfall amounts still remain a bit on the
uncertain side...although nearly all guidance solutions
(EURO/GFS/NAM/ensembles) have trended upward over the last 2
forecast cycles...now suggesting somewhere in the 3 to 4 inch
storm total amount through the day Tuesday (with some guidance
solutions in the 4 to 5 inch range). Outside of the more
localized summertime convective events...cannot remember the last
time we`ve seen that amount of rainfall in a 36 to 48 hour
stretch...so the impacts are a bit uncertain even with our sandy
soil conditions. But given the rainfall magnitude potential...and
upon collaboration with GRR/DTX...plan to hoist a flood watch for
all of northern lower Michigan valid from this afternoon through
Tuesday morning.

&&

.SHORT TERM...(Tuesday through Wednesday)
Issued at 347 AM EDT Mon Oct 23 2017

...Cool with more rain showers and maybe even snow showers...

So it looks like the ECMWF had the correct idea all along with the
phasing as the GFS/NAM are now fully on board. So the general
consensus is for the deepening area of low pressure to start out
near the Straits region early Tuesday then loop back around and head
southwest Tuesday afternoon before heading slowly northeast Tuesday
night. Models do vary on the exact details of how far south the
surface low tracks and how deep it is. Regardless, strong
deformation axis continues to provide impressive lift through the
day Tuesday (mainly across the southwestern forecast area). Model
qpf is on the order of an additional one half to one inch Tuesday
with perhaps another quarter to half inch Tuesday night. In
addition, wrap around rain with lake enhancement is expected into
Wednesday as well. Looking at thermal profiles, a mix with or an
eventual change over to snow may occur overnight Tuesday into
Wednesday. Would not be shocked if the higher terrain even picked up
a slushy inch or two of snow accumulation. It will be windy during
much of this time as well with gusts reaching 25 to 30 mph. The
additional rain may lead to areas of urban, small stream and river
flooding. Temperatures will be chilly with mainly 40s Tuesday and
Wednesday and lows in the 30s.

.LONG TERM...(Wednesday night through Sunday)
Issued at 347 AM EDT Mon Oct 23 2017

Lake effect rain or mixed rain and snow showers may linger into
Wednesday evening but warm advection quickly kicks in decreasing
over lake instability. A clipper system then tracks southeast toward
northern Michigan during the late Thursday into Friday timeframe.
This will lead to increasing rain shower chances late Thursday with
a shot of colder air to follow for Thursday night into Friday
leading to more rain showers which may mix with or change over to
snow (sorry but the warm temperature party looks pretty much over).
Another clipper and associated colder air looks to drop into
northern Michigan over the weekend bringing more rain/snow showers.

&&

.AVIATION...(For the 12Z TAFS through 12Z Tuesday morning)
Issued at 643 AM EDT Mon Oct 23 2017

Low pressure over the mid Mississippi River Valley will advance up
through the Great Lakes through tonight. Persistent and...at
times...heavy rainfall will continue along the track of this
system up through northern lower Michigan. This will bring solid
MVFR to IFR conditions to the terminal sites through the upcoming
TAF period.

Lighter winds today...but winds will increase substantially
tonight as the storm system nears the region.


&&

.MARINE...
Issued at 427 AM EDT Mon Oct 23 2017

Low pressure in the lower Mississippi River Valley will deepen and
move up through the Great Lakes tonight through Tuesday night.
This system will bring gale force gusts to many nearshore areas
through Tuesday night. Otherwise...a prolonged period of rain and
cool weather is anticipated through the week.


&&

.APX WATCHES/WARNINGS/ADVISORIES...
MI...FLOOD WATCH from 2 PM EDT this afternoon through Tuesday morning
     for MIZ016>036-041-042.
LH...GALE WARNING from midnight tonight to midnight EDT Tuesday night
     for LHZ348-349.
     SMALL CRAFT ADVISORY from 8 PM this evening to midnight EDT
     Tuesday night for LHZ345>347.
LM...SMALL CRAFT ADVISORY from 8 PM this evening to 8 PM EDT Tuesday
     for LMZ341.
     GALE WARNING from midnight tonight to 6 AM EDT Wednesday for
     LMZ323-342-344>346.
LS...SMALL CRAFT ADVISORY from 8 PM this evening to 8 PM EDT Tuesday
     for LSZ321-322.
&&

$$

UPDATE...JZ
NEAR TERM...BA
SHORT TERM...AS
LONG TERM...AS
AVIATION...BA
MARINE...BA



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