textproduct: Cleveland

WHAT HAS CHANGED

Rain chances and amounts for tonight have increased, especially across northern portions of the area. Little change to the "big picture" Thursday through Saturday, though some minor adjustments were made to precip chances/amounts/types and temperatures.

KEY MESSAGES

1) After a dry day today, a period of rain is expected across the entire area tonight into early Thursday morning. It turns breezy and cooler on Thursday as occasional showers continue.

2) Lake effect showers continue Thursday night into the weekend as western portions of the area dry out. Snow will mix in at times, especially away from Lake Erie, though the risk for impactful accumulations remains low.

3) Dry weather with a slow warming trend early next week.

DISCUSSION

KEY MESSAGE 1... Mid-upper level clouds will stream in today ahead of a digging trough and developing low pressure, though we should remain rain-free through the day with afternoon highs of 55-60.

This forecaster thinks it's fair to say "the party"...in this case, a prolonged period of relatively warm and dry weather to start the fall...is over starting this evening. A cold front will sink south across the area late this afternoon into this evening, with deepening low pressure tracking just to our south across the Upper Ohio Valley overnight tonight. As guidance finally converges on the final track/intensity of this low, rain chances and amounts have been nudged up a bit as it's looking like the expected swath of rain just north/northwest of the low will track right across our forecast area. This will be a rather compact system moving through fairly quickly, which will limit rain amounts to a point. However, there will be a brief period of low-mid level frontogenesis as thermal packing takes place just north-northwest of the low tonight which should support more organized/banded rain. There may be just a touch of elevated instability as well, which can support a bit of a convective component. The forecast has a swath of 0.20-0.40" of rain focused on a Findlay-Cleveland-Erie line through early Thursday with a bit less outside of that. Locally higher amounts over 0.50" are possible, with guidance still disagreeing slightly on exactly where the greatest swath of rain tracks. Lows tonight are expected to fall into the low-mid 40s.

Unsettled weather continues area-wide beneath the deepening upper-level trough on Thursday as low pressure transfers to off the northern Mid Atlantic coast. As temperatures aloft continue cooling through Thursday and sufficient synoptic moisture lingers, lake effect showers are expected to develop early in the morning and continue through the day. With initially northeast winds the lake effect will focus south- southwest of the lake, farther west/southwest into North Central Ohio than is normal. Outside of the lake effect, an inverted surface trough extending into the Great Lakes behind the departing low pressure is expected to drop across the area Thursday afternoon or evening as an embedded shortwave aloft also rotates through the region. This will likely bring a more organized batch of showers to the entire area and also cause ongoing lake effect to briefly enhance with the trough passage. Additional rain amounts Thursday will generally be under a quarter-inch, though it's possible locations near and just southwest of Cleveland see more due to lake enhancement. Temperatures will rise no more than a few degrees and may even cool later in the afternoon, with highs staying in the 40s. It will be blustery with northerly winds gusting 20-30 MPH.

KEY MESSAGE 2... Once the inverted trough sinks south of the area Thursday evening, shower activity is expected to become primarily lake- driven for the end of the week and into the weekend. Upper troughing will be deepest overhead Thursday night and Friday before slowly weakening and moving east this weekend. Initially north-northeast winds Thursday night are expected to gradually back more northerly on Friday and more northwesterly through the weekend. Conditions will be most conducive to lake effect overnight Thursday night through early Saturday beneath the heart of the upper trough. During this timeframe, 500mb temperatures will bottom out at around -30C over 12-15C lake waters as synoptic moisture lingers. The mid-levels will start to gradually warm and dry on Saturday, though it is expected to be a slow ramp down of lake effect with activity not expected to completely end until Sunday night or early Monday when the surface ridge axis builds into the area. Outside of the lake effect, there may still be a few sprinkles or light showers across Northwest OH on Friday beneath the deep troughing aloft. Conditions should trend completely dry across western portions of the area for the weekend.

The main focus for more organized/intense lake effect is expected to be a connection to Lake Huron. This connection is expected to initially set-up west of Cleveland (and perhaps briefly as far west as Sandusky and Mansfield) Thursday night into Friday. From there, it will gradually shift east across the Cleveland metro area later Friday into early Saturday and into the more traditional snowbelt of far Northeast OH and Northwest PA through the weekend. Outside of this connection there will be some less-organized lake effect at times. The most precip will tend to fall in the higher terrain immediately downwind of the lake given the short fetch. Lake effect will ebb and flow in terms of organized and intensity through the event as various subtle vort maxes or shortwaves rotate through. There are hints that lake effect may peak in intensity early Friday, and then again late Friday afternoon through early Saturday.

In terms of precip types, it will become cold enough aloft Thursday night through Saturday night for snow to mix in with the rain, especially away from the lake and during the overnight and morning hours. The main uncertainty involves milder surface temperatures, owing to a lack of Arctic influence and modification from the mild Great Lake waters. In general, am expecting temperatures Thursday, Friday, and Saturday nights to bottom out in the low-mid 30s away from the lake where lake effect clouds/showers continue. It will be difficult to see temperatures dip to freezing or below where lake effect continues, though a few spots above 1200' elevation may. Chillier sub-freezing values are more likely across western portions of our area each night where clouds may dry clearing out at times. Locations closer to the lake will struggle to fall below the upper 30s or lower 40s. Daytime highs will only reach the upper 30s and lower 40s on Friday, before inching up a degree or two each day but staying in the 40s Saturday and Sunday.

Given strong instability and cold air aloft through early Saturday, more convective lake effect will be able to mix with graupel or wet snow even during the daytime hours and potentially near the lakeshore as well. However, given the marginal low-level thermals, the greatest potential for precip to mix with or change to all snow for a length of time will be during the overnight/morning hours and away from Lake Erie. The odds for impactful accumulations remain quite low and the official forecast has no more than very light amounts away from the lake. However, it's possible measurable snow occurs in parts of the area, mainly beneath any stronger Lake Huron connection early Friday and again Friday night into early Saturday. Amounts would not be more than a localized inch or two, but given the conducive setup and convective nature amounts higher than what we can put in the forecast this far in advance are possible. Outside of this more intense Huron-connected band, it's possible the higher terrain east of I-79 in Pennsylvania is cold enough to see a light dusting of snow one of those nights.

KEY MESSAGE 3... There's good agreement that this weekend's trough will continue exiting east the first half of next week as a ridge builds east out of the central U.S. Surface high pressure is likely to move overhead the first half of next week, leading to a period of dry and tranquil weather as temperatures very slowly moderate.

AVIATION /06Z Wednesday THROUGH Sunday/

VFR is expected through Wednesday evening before conditions start to deteriorate as showers move in from the west. Rain will likely reach KTOL/KFDY shortly after 00Z and reach the eastern fringe of the CWA towards the end of the TAF period. There's still some uncertainty in the placement of rain so amendments to refine the timing may be needed. Either way, ceilings and visibilities will gradually lower in precip with MVFR likely at western terminals by 06Z Thursday. Winds will be light through Wednesday evening before beginning to shift to the north/northeast and increasing to 5 to 10 knots after 00Z Thursday.

Outlook...Non-VFR will be likely with low ceilings and periods of rain showers Thursday and Friday, then lingering across Northeast Ohio and Northwest Pennsylvania through the weekend. Some wet snow showers may also be possible at the end of the week and weekend. Wind gusts to 35 mph are possible on Thursday.

MARINE

A cold front will cross the lake late this afternoon, with deepening low pressure tracking through the upper Ohio Valley tonight. A trough will linger behind the departing low through the end of the week before high pressure slowly builds in from the west to end the weekend and start next week. After a tranquil day today, northeast winds will ramp up to 15-20kt tonight. Winds will shift more northerly and increase to 20-30kt on Thursday. Waves are expected to peak at 4 to 7 feet Thursday into Thursday night. Winds will gradually shift more northwest Friday and through the weekend, remaining elevated at 15-25kt through early Saturday before slowly relaxing through the weekend. We will need high-end Small Craft Advisories for all nearshore waters starting tonight or early Thursday. The risk of a gale on Thursday remains non-zero but under 20%. There is some uncertainty regarding how long the advisories will need to run and the lake will be tranquil through the day today, so will let the day shift take a look at one more run of guidance before hoisting the SCAs.

CLE WATCHES/WARNINGS/ADVISORIES

OH...None. PA...None. MARINE...None.