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Jan 20th snow event


Thundersnow12

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Here's my call for MKE, .38" liquid for 6 inches...lock it in.

I would agree, MKE def in the 5-7" range. Chicago has me worried though now, earlier this morning I thought 5-7" there too. However might be more 4-6" and along I-80 maybe less. Still a fluid situation though.

Also Grand Rapids must be discounting Euro as they went with a WWA for bottom 3 tiers only...

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I would agree, MKE def in the 5-7" range. Chicago has me worried though now, earlier this morning I thought 5-7" there too. However might be more 4-6" and along I-80 maybe less. Still a fluid situation though.

Also Grand Rapids must be discounting Euro as they went with a WWA for bottom 3 tiers only...

I80 is pretty far south, I think 88 North has always been the place to be for Illinois and now possibly 90 north.

Worth mentioning that the Iowa counties under warning get very little from this run.

death gradient

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LOT

FORECAST SOUNDINGS FROM VARIOUS MODELS CONTINUE TO SHOW A DEEP

ISOTHERMAL LAYER HOVERING AROUND -10C. HOWEVER...FORECAST TIME

HEIGHT CROSS SECTIONS DO SUGGEST THAT UVVS WILL BE STRONG WITHIN THE

DENDRITIC GROWTH ZONE BETWEEN ROUGHLY 600-500MB WITH FAIRLY LIGHT

WINDS ALSO TENDING TO FAVOR HIGHER THAN AVERAGE SNOW TO LIQUID

RATIOS. ADMITTEDLY OUR SKILL IN PREDICTING SNOW:LIQUID RATIOS IS

LOW...BUT THIS EVENT DOES APPEAR TO HAVE THE LOOKS OF A HIGHER RATIO

EVENT. OTHER THAN THE VARIOUS WRF AND HI-RES MESOSCALE

MODELS...FORECAST MAX QPF HAS REMAINED CONSISTENTLY BETWEEN

0.35-0.50" WITHIN THE BAND OF HEAVIEST SNOW WHICH IS STILL LOOKING

TO SET-UP OVER FAR NORTHERN ILLINOIS.

HAVE BEEN HEMMING AND HAWING ALL MORNING LONG TRYING TO DECIDED

WHAT TO DO WITH THE ONGOING WINTER STORM WATCH. OVERALL...THIS

SYSTEM REALLY HAS THE LOOKS OF A SOLID ADVISORY EVENT AS IT IS A

LOW AMPLITUDE OPEN WAVE THAT IS EVEN DAMPENING SOMEWHAT AS IT

MOVES VERY QUICKLY EASTWARD. MANY OF THE HIGHER-RES WRFS CONTINUE

TO SPIT OUT HIGHER QPFS AND AM FAIRLY CONFIDENT THAT THESE NUMBERS

ARE TOO HIGH. PROBABLY THE BIGGEST WILD CARD WHICH COULD

POTENTIALLY PUSH SOME AREAS OVER THE EDGE INTO WARNING CRITERIA IS

THE SNOW:LIQUID RATIOS. HAVE GENERALLY GONE WITH 12-15:1 RATIOS IN

THE GRIDS NORTH OF I-80...WHICH SHOULD THESE TURN OUT TO BE TOO

CONSERVATIVE COULD RESULT IN SOME AREAS EXCEEDING 6 INCHES...BUT

THIS WILL LIKELY BE MORE OF A NOW-CASTING SHORT-FUSED UPGRADE TYPE

ISSUE.

AS ALLUDED TO IN THE BRIEF LATE MORNING AFD UPDATE THERE LOOKS TO BE

A VERY SHARP CUT OFF TO THE PRECIP ALONG THE SOUTHERN EDGE. FAR

SOUTHERN PORTIONS OF THE CWA WILL LIKELY REMAIN GENERALLY DRY

THROUGH THE DAY TOMORROW WITH A TIGHT GRADIENT BETWEEN ADVISORY

CRITERIA SNOWFALL AND LITTLE IF ANY ACCUMULATION. GRADIENT IN THE

CURRENT SNOW GRIDS AND FORECAST SNOW GRAPHICS IS LIKELY TOO BAGGY

BUT ABOUT AS REASONABLE OF A REPRESENTATION AS IS POSSIBLE AT THIS

DISTANCE.

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LOT

FORECAST SOUNDINGS FROM VARIOUS MODELS CONTINUE TO SHOW A DEEP

ISOTHERMAL LAYER HOVERING AROUND -10C. HOWEVER...FORECAST TIME

HEIGHT CROSS SECTIONS DO SUGGEST THAT UVVS WILL BE STRONG WITHIN THE

DENDRITIC GROWTH ZONE BETWEEN ROUGHLY 600-500MB WITH FAIRLY LIGHT

WINDS ALSO TENDING TO FAVOR HIGHER THAN AVERAGE SNOW TO LIQUID

RATIOS. ADMITTEDLY OUR SKILL IN PREDICTING SNOW:LIQUID RATIOS IS

LOW...BUT THIS EVENT DOES APPEAR TO HAVE THE LOOKS OF A HIGHER RATIO

EVENT. OTHER THAN THE VARIOUS WRF AND HI-RES MESOSCALE

MODELS...FORECAST MAX QPF HAS REMAINED CONSISTENTLY BETWEEN

0.35-0.50" WITHIN THE BAND OF HEAVIEST SNOW WHICH IS STILL LOOKING

TO SET-UP OVER FAR NORTHERN ILLINOIS.

HAVE BEEN HEMMING AND HAWING ALL MORNING LONG TRYING TO DECIDED

WHAT TO DO WITH THE ONGOING WINTER STORM WATCH. OVERALL...THIS

SYSTEM REALLY HAS THE LOOKS OF A SOLID ADVISORY EVENT AS IT IS A

LOW AMPLITUDE OPEN WAVE THAT IS EVEN DAMPENING SOMEWHAT AS IT

MOVES VERY QUICKLY EASTWARD. MANY OF THE HIGHER-RES WRFS CONTINUE

TO SPIT OUT HIGHER QPFS AND AM FAIRLY CONFIDENT THAT THESE NUMBERS

ARE TOO HIGH. PROBABLY THE BIGGEST WILD CARD WHICH COULD

POTENTIALLY PUSH SOME AREAS OVER THE EDGE INTO WARNING CRITERIA IS

THE SNOW:LIQUID RATIOS. HAVE GENERALLY GONE WITH 12-15:1 RATIOS IN

THE GRIDS NORTH OF I-80...WHICH SHOULD THESE TURN OUT TO BE TOO

CONSERVATIVE COULD RESULT IN SOME AREAS EXCEEDING 6 INCHES...BUT

THIS WILL LIKELY BE MORE OF A NOW-CASTING SHORT-FUSED UPGRADE TYPE

ISSUE.

AS ALLUDED TO IN THE BRIEF LATE MORNING AFD UPDATE THERE LOOKS TO BE

A VERY SHARP CUT OFF TO THE PRECIP ALONG THE SOUTHERN EDGE. FAR

SOUTHERN PORTIONS OF THE CWA WILL LIKELY REMAIN GENERALLY DRY

THROUGH THE DAY TOMORROW WITH A TIGHT GRADIENT BETWEEN ADVISORY

CRITERIA SNOWFALL AND LITTLE IF ANY ACCUMULATION. GRADIENT IN THE

CURRENT SNOW GRIDS AND FORECAST SNOW GRAPHICS IS LIKELY TOO BAGGY

BUT ABOUT AS REASONABLE OF A REPRESENTATION AS IS POSSIBLE AT THIS

DISTANCE.

Very well put quality discussion from LOT

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DTX Thoughts....

Dynamics for this event will primarily be that of moist isentropic

ascent along a gradually sloped stationary frontal boundary. Models

suggest that the 290k surface will activate during the afternoon

before transitioning down to the 285k surface as a subtle Theta-E

ridge rolls into southeastern Michigan during the evening.

Saturation will be deep...with available mixing ratios from 2-3

g/kg. Given the broad signal of the ascent within x

sections...feeling is a widespread accumulating snowfall is likely

for virtually all of the County Warning Area. There are negatives...the big one

being quick system motion...the second being the overall lack of a

strong or consistent frontogenesis feature (models do suggest some

feature during the afternoon/but then quickly transition better fgen

over northern Indiana. The magnitude and structure of the

deformation field should allow the accumulating snow to fall even

across portions of Midland and Bay counties. Snow ratios have

provided a wrinkle with the traditional Cobb technique suggesting

some snow ratios as low as 8:1 across the far south. The only guess

at that is it may be keying off a riming layer at -3 to -4c at

roughly 7 kft above ground level. Otherwise...southeastern Michigan remaining

comfortably on the cool side of the stationary front...along with in

house snow ratio ensemble technique suggests an event average

snow ratio to fall in the 11:1 to 14:1 range higher north/lower

south.

Add this all up...the going forecast will carry ranging quantitative precipitation forecast amounts

from around .1 across the far north to around .3 inch across the

southern 4 counties. With the snow ratios mentioned above...this

yields expected snow amounts of between 3 to 5 inches for the

southern 4 counties...2 to 4 inches between I 69 and M 59...and

generally 1 to 3 inches north of I 69. The snow is expected to push

in after 2pm and exit the area by 2 am. The highest impact snow

rates are expected to move in...during the evening commute. A

tighter consensus on timing in the 00z cycle will be something to

watch. With late period 2 to period 3 timing of the event...no

headline decisions were made.

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I think most of Chicagoland will be fine. I see the 18z NAM as the northern extreme in this setup. It's hard to imagine it going any farther north given the airmass in place and lack of a strong/well defined wave so I'd anticipate a southward bump on the 00z run if anything.

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I think most of Chicagoland will be fine. I see the 18z NAM as the northern extreme in this setup. It's hard to imagine it going any farther north given the airmass in place and lack of a strong/well defined wave so I'd anticipate a southward bump on the 00z run if anything.

I really miss seeing those LAF sups in your picture.

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You can see the lake effect/enhancement nicely at this map. - into Chicago.

IMO, LE looks to add next to nothing, boundary level wind are only favorable for a super brief period and never all that strong. Unless wee see freak and unpredictable mesolow develope and move west, the lake won't be a factor.

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Well I'd rather wait till the 0z runs tonight and 12z runs tomorrow.

Any thoughts thus far.

I'm going for 0.5 to 1.5" not including LES.

Lets hope it shifts north.

I'll tell you what. I'll suspend my edict to toss the NAM for 20 minutes while we digest the 18z GFS. Barring a substantive shift with that model, I think this is just a typical garbage 18z NAM run.

I concur with the amounts you posted.

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