textproduct: Cleveland

WHAT HAS CHANGED

Increased POP's and QPF for a band of snow showers, some steady to heavy, along an reinforcing Arctic front sweeping SE'ward through our region. These snow showers are the result of low- level convergence/moist ascent along the front releasing at least weak potential instability in the lowest ~1 km AGL. The front and associated snow showers will continue to advance SE'ward and should exit the rest of our region by midday today, give or take one hour. Fresh snow accumulations of one inch or less are expected with these snow showers.

KEY MESSAGES

1) A major winter storm will impact the entire region Saturday night into Monday morning bringing widespread accumulating snowfall combined with single digit and sub-zero wind chills. Hazardous travel is expected, especially on Sunday.

2) Wind chills of 10 to 15 below zero today and actual air temperatures below zero tonight into Saturday morning have kept a Cold Weather Advisory in place for this period.

3) Prolonged cold temperatures will last through next week with frequent bouts of sub-zero wind chills and light snow.

DISCUSSION

KEY MESSAGE 1... The first widespread "cross country" winter storm with plentiful moisture from the Gulf in about 4 years will impact the entire region Saturday night into Monday morning.

Synoptic Overview: Infrared satellite and water vapor loops early this morning show the early stages of this storm coming together, with a closed southern stream mid/upper low off Baja California and northern stream mid/upper jet energy diving into the northern Rockies on the western periphery of the broad central and eastern North American trough. As the southern stream mid/upper low moves into Mexico today and tonight, it will start to phase with the aforementioned northern stream energy. This will encourage strong warm/moist advection from an open Gulf across the southern Plains tonight into Saturday morning, leading to widespread precip breaking out beneath strong isentropic ascent across the southern Plains, Lower and Mid Mississippi Valleys, and Tennessee Valley. During the day Saturday, another piece of northern stream jet energy will dive through the Rockies and northern Plains, with the associated shortwave phasing with the southern stream shortwave. This second phasing is what will really accelerate the surface cyclogenesis along the Texas and Louisiana Gulf coasts by Saturday evening. The deepening surface low will then lift across the Tennessee and Lower Ohio Valleys Sunday and offshore of roughly the Jersey shore by Monday morning, with deep mid/upper troughing and associated pool of arctic air then reloading across the central and eastern CONUS in its wake. As this low lifts northeastward Saturday night through Monday morning, the aforementioned large shield of precip will spread across the region. This will begin late Saturday evening, peak during the day Sunday, then gradually taper off from west to east late Sunday night into Monday.

Precip Type/Snow Amounts/Impacts: The large mid/upper trough combined with strong 1040-1050 arctic high pressure at the surface over the Upper Midwest and Great Lakes ahead of this system Saturday will keep plenty of cold air in place for precip to fall as strictly snow with this storm. We are 100% confident that any mixed precip will be south of our region. Timing remains consistent on snow overspreading the region from southwest to northeast late Saturday evening, with the heaviest snow falling on Sunday before slowly tapering off Sunday night and Monday from west to east. The biggest challenge with the forecast continues to be where the axis of heaviest snow will set up. The past several model cycles have seen a NW shift in the track of the surface low and resultant axis of heaviest snowfall, and there is still time for further refinements to the track as model guidance resolves the aforementioned phasing. Northern and southern stream jet phasing is known to pull systems farther NW than models initially indicate, so this NW trend has not been surprising. With this being said, there were no notable changes to snowfall amounts with this morning's update, and it still looks like a solid 6-12 inches for most of the region. Probabilistic guidance continues to paint the highest probabilities for greater than 8" of snow in 24 hours (60-70%) over our SE Counties from Mt. Vernon to Meadville, with 30-40% probabilities in NW Ohio from Findlay to Toledo. If the low trends farther NW, then the heavier snow will reach into NW Ohio, but given the lower confidence at this point, kept that area in a Watch. Given the aforementioned higher confidence further E and SE, upgraded the rest of the area to a Warning. Since this will be a widespread and long duration snow, travel will be heavily impacted everywhere with snow covered roads. It will not be a very windy system, with NE winds averaging 8 to 15 knots through Sunday (highest in NW Ohio and near the lake), but the very cold temperatures will lead to a dry snow that will still blow around easily, especially as NW winds increase to 15-25 knots on the backside of the system Sunday night and Monday.

Temperatures/Wind Chills: As stated, arctic air will be well-established ahead of this system and remain in place through its duration. Temperatures in the single digits Saturday night, teens and 20s Sunday, and single digits/low teens Sunday night into Monday will lead to below zero wind chills at night and single digits during the day. Anyone traveling should have a winter weather kit with warm blankets, food, water, and portable chargers since the extreme temperatures will worsen the impacts for stranded motorists. Travel is strongly discouraged for this event.

KEY MESSAGE 2... Before the much talked about storm, we already have to deal with bitter cold. An arctic cold front will continue to push east of the region this morning. A westerly boundary layer flow in the wake of the front over the next few hours combined with lingering moisture and strong cold air advection has generated lake-effect snow showers over far NE Ohio and NW PA. The lake is mostly ice covered, so this will keep the activity light, but boosted POPS for 1 to 2 inches of snow this morning. Another surface trough looks to push across the lake in the 12-14Z timeframe, and that will bring a burst of lake enhanced snow showers to most of the lakeshore. This could bring a few tenth of an inch as far west as Lorain County. Most of NE Ohio will see a few tenths to up to 0.5 inch this morning, with those 1-2 inch amounts mainly confined to northern Ashtabula and Erie Counties. Boundary layer flow will turn NW behind the surface trough late this morning through the afternoon along with strong arctic high pressure building in from the NW, so expect lingering snow showers to end by late afternoon or early evening.

Temperatures will steadily fall through the day today, so made a non-diurnal temperature curve. Expect temperatures to be in the single digits by late morning through the afternoon. This combined with winds of 15-25 knots will lead to wind chills of -10 to -15 F. The winds will become light tonight as the high builds in, but actual air temperatures will tank into the -3 to -8 F range, with some sheltered valley locations of NE Ohio and NW PA possibly falling below -10 F. Temperatures will remain below zero through Saturday morning. The Cold Weather Advisory covers the combination of wind chills today and below zero actual air temperatures tonight and early Saturday.

KEY MESSAGE 3... Arctic air will remain in place all of next week as deep mid/upper troughing remains entrenched across central and eastern North America downstream of massive ridging off the West Coast extending into Alaska. This will keep a strong mid-level vortex in place near Hudson Bay, pinwheeling a series of reinforcing shortwaves and associated cold fronts through the region. Each one of these weak disturbances will bring light synoptic snows, as well as periods of light lake-effect snow. The details of these clipper-type systems are difficult to pinpoint this many days out, but the biggest impact will be prolonged cold with periods of below zero wind chills. High temperatures will not climb out of the teens all week, with frequent lows in the single digits to below zero.

AVIATION /18Z Friday THROUGH Wednesday/

Scattered light lake effect snow showers continue across Northeast Ohio. Visibilities may briefly drop to one mile in snow showers along with MVFR visibilities through about 21Z then should diminish as the air continues to dry out. Skies are likely to clear out between 22-03Z across the snowbelt. High clouds will begin to move in overnight through Saturday but will be VFR through the TAF period. Northwest winds will gust to 25 knots at times this afternoon, with gusts dropping off towards 00Z and winds becoming 7 knots or less while veering to the northeast through Saturday morning.

Outlook...Widespread snow spreads moves in from the south Saturday night, before tapering off Monday morning. Snow will be moderate in intensity through the event but high snowfall totals are expected. Non-VFR with lake effect snow showers will be possible in Northeast Ohio and Northwest Pennsylvania into Tuesday.

MARINE

West-northwest flow will continue to diminish through today and tonight as high pressure builds into the region, with nearly calm conditions on Saturday.

East-northeast flow of around 15-20 knots develops on Sunday, before becoming northwest on Monday and then southwest on Tuesday. There is a very low chance for gales (5-10%) with the southwesterly flow on Tuesday. There is also a low chance for low water in the western basin as well.

Ice on Lake Erie (which is mostly ice-covered at this point) will continue to thicken/expand through next week as several bouts of cold air impact the region. Periods of stronger winds, such as this morning and on Monday/Tuesday, will limit ice growth and cause ice to shift around.

CLE WATCHES/WARNINGS/ADVISORIES

OH...Cold Weather Advisory until 7 AM EST Saturday for OHZ003- 006>014-017>023-027>033-036>038-047-089. Winter Storm Watch from Saturday evening through Monday morning for OHZ003-006>008-017. Winter Storm Warning from 7 PM Saturday to 10 AM EST Monday for OHZ009>014-018>023-027>033-036>038-047-089. PA...Cold Weather Advisory until 7 AM EST Saturday for PAZ001>003. Winter Storm Warning from 7 PM Saturday to 1 PM EST Monday for PAZ001>003. MARINE...None.