Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

FXUS63 KIWX 221156

Area Forecast Discussion
National Weather Service Northern Indiana
656 AM EST Mon Jan 22 2018

Issued at 657 AM EST Mon Jan 22 2018

Periods of rain can be expected today as a large storm system across 
the central part of the country tracks eastward. A warm front 
lifting northward ahead of this system will provide very mild 
conditions today with highs in the lower to mid 50s. Colder air will 
work back into the region today and Tuesday with rain showers 
changing over to some snow showers along with gusty west winds. 
Little if any snow accumulation is expected on Tuesday however.
Conditions will dry out Tuesday night and Wednesday with near
seasonable temperatures before temperatures moderate once again
for Thursday and Friday.


.SHORT TERM...(Today and Tonight)
Issued at 347 AM EST Mon Jan 22 2018

Early morning fog, periods of rain today, and very mild 
temperatures will be the main weather stories for the short term 

Broad area of generally light rain showers developed earlier during 
the overnight hours at leading edge of stronger low level jet with 
axis of decent low level mass convergence. This axis of forcing has 
now migrated across southern Lower Michigan and will continue to 
lift northeast over the next few hours. Rainfall amounts with this 
band appear to be in the 0.1 to 0.2 inch range. Additional showers 
have developed across west central Indiana into central Illinois 
in broader warm/moist advection wing forcing with upstream system.
Area of heavier showers and isolated thunderstorms linger back 
across central/west central Illinois where stronger frontal 
forcing and more impressive upper dynamics are in place. Near term
progs of of mid-upper level Q-vector convergence take strongest 
upper forcing across northeast Illinois into western Lower 
Michigan, just grazing far northwest portions of the area. 

Additional scattered showers will likely develop across the area 
over next several hours due to broad advective forcing, but for 
remainder of the area, will likely have to wait for this more 
frontally forced precip and approach of upper trough for more 
organized area of rain to shift west to east across the area. Have
continued to slightly lower storm total rainfall forecast amounts
due to glancing blow from initial stronger mid/upper forcing.
Highest amounts still expected across the far north/northwest 
which will experience some contribution of stronger upper forcing 
clipping the southern Great Lakes. Storm total rain amounts near 
an inch are possible across the extreme northwest. A brief window 
of weak elevated CAPE also may enhance rain rates in the 11Z-15Z 
timeframe across these locations. Duration of these weak elevated 
moisture profiles will be limited however. With higher end precip 
looking less likely at this point, hydro impacts should be limited
to the possibility of some minor flooding at a few forecast 
points later this week.

Other concern this morning is on lingering dense fog. Over past hour 
or two, starting to see more dramatic effects of northward lifting 
warm sector/warm front, with rapidly improving visibilities 
across central Indiana, and now working into southern sections of 
the forecast area as of 08Z. Will allow dense fog advisory to 
expire at 09Z for southern portion of existing advisory, with just
a brief extension to 12Z for the far north, although vsbys likely
to rapidly improve after 10Z even across these locations as warm 
front makes more steady progress northward.

Dry slot to overspread the area late morning into the afternoon as 
system occludes with lull in precip coverage and likely transition 
to drizzly type precip before wrap around moisture and mid/upper 
level height minimum tracks across central Illinois this evening. 
Vort lobe swinging through the parent upper circulation will result 
in scattered-numerous rain showers tonight.

In terms of temperatures, very mild conditions today as region 
briefly gets in more established warm sector, with temps probably in 
the lower to mid 50s most locations by mid morning. Lows tonight 
will  drop back into the 35 to 40 degree range with eventual 
transition to rain/snow showers and then to snow showers for


.LONG TERM...(Tuesday through Sunday)
Issued at 347 AM EST Mon Jan 22 2018

Unsettled conditions persist into Tuesday as wrap around deformation 
precip continues. Several factors still appear to be in place to 
limit snow accumulations. Near sfc wet bulbs will remain on the high 
side, and wet nature of snow should limit ratios. Mid level moisture 
profiles in DGZ also becoming increasing marginal, with transition 
to synoptic scale forcing for descent mid/upper levels later Tuesday 
afternoon. If any snow accumulations do occur Tuesday, totals should 
be generally less than inch. Cannot completely rule out precip 
ending as some very patchy light freezing drizzle given DGZ 
saturation issues noted above, but expectation at this point is that 
if this occurs, supported precip would be very light and of little 
to no consequence.

The middle of the week will feature seasonable temps before another 
moderating trend for Thursday and Friday. A weak ridge-riding wave 
is expected to dig across the Great Lakes on Wednesday but moisture 
profiles will be quite meager and will continue with just slight 
chance snow shower mention downwind of Lake Michigan.

Precip chances ramp up again for the Fri-Sun period as a more 
substantial eastern Pacific trough shifts across western CONUS 
pushes across the region. Cold advection behind this trough should 
be short-lived as flow deamplifies preceding next Pacific wave for 
after this forecast valid period.


.AVIATION...(For the 12Z TAFS through 12Z Tuesday Morning)
Issued at 654 AM EST Mon Jan 22 2018

Expect a brief period of improved conditions through early this 
morning (KSBN) and early afternoon (KFWA) as we are in the warm 
sector of the low pressure system. Expect the cold front to 
arrive, impacting KSBN first (with the heaviest precipitation) and
then KFWA later today. There could be some isolated, brief 
showers before then but expect them to have limited impacts. As 
the front passes we could see conditions drop to IFR (especially 
at KSBN) given the more moderate rain observed along the incoming
line. Expect mainly MVFR conditions in the wake of the front, with
scattered light rain showers overnight. LLWS continues through 
this morning.


MI...Dense Fog Advisory until 7 AM EST this morning for MIZ080-081.

OH...Dense Fog Advisory until 7 AM EST this morning for OHZ001-002.

LM...Dense Fog Advisory until 7 AM EST this morning for LMZ043-046.



SHORT TERM...Marsili
LONG TERM...Marsili

Visit us at

National Weather Service Glossary of Abbreviations