While Rain Is Expected To Dominate Saturday Night Into Sunday In Most Locations, Prior To A Change To Light Snow, Freezing Rain Remains A Possibility At Upper Elevations Within The High Knob Massif.
Update_10:30 PM Saturday
Icing On Eagle Knob of High Knob Massif – Saturday Evening_January 12, 2019
A major ice storm in mid-November 2018 caused extensive tree damage at highest elevations in the High Knob Massif, blocking roads and severely damaging some trees.
While I do not expect this event to be nearly that severe, it only takes a little bit of ice to cause trouble.
Caution is advised for travelers into high elevations of the High Knob Massif where icing has occurred this evening ( January 12 ) at upper elevations, mainly at elevations above 3300 feet, along State Route 619 and adjoining roadways.
A complicated, messy winter storm of the Miller B type is expected to begin impacting mountain area conditions by early Saturday ( January 12 ).
Cold air in place will initially support all snow before a layer of above freezing air aloft moves over the Tennessee Valley and southern Appalachians to force a change in precipitation type to a cold, nasty rain for most ( freezing rain remaining possible at upper elevations within the High Knob Massif ).
Cloud bases will drop and precipitation will change back to snow by later Sunday into Monday morning with a rather prolonged period of freezing fog ( riming ) possible at the upper elevations along and north of the High Knob Massif-Tennessee Valley Divide ( mid-elevations above 2500 feet could also be impacted ).
Cloud Bases Are Expected To Lower On Northerly Upslope Flow With Dense Fog Changing To Freezing Fog And Becoming Widespread At Upper Elevations Sunday Into Monday. Snow amounts will be light.
Former Alerts
A Period Of Snow Will Develop During The Predawn-Morning Hours Of Saturday Before A Break Develops In Advance Of Another Wave Of Moisture With Mixed Precipitation By Later Saturday. Due To The Current Arctic Air Mass Hazardous Road Conditions Will Be Likely Early Saturday. Caution Is Advised.
Mountain Area Forecast ( Jan 11-14 )
Friday Night Into Saturday Morning
Becoming cloudy with snow developing from high to low elevations into the predawn-morning as the air saturates from the top downward. Light winds, then SSE-SW at 5-10 mph, with higher gusts, on mid-upper elevation mountain ridges toward morning. Temps dropping into the 20s to around 30 degrees, with lower wind chills on higher ridges by morning.
Saturday Morning Through The Afternoon
Snow becoming mixed with or changing to sleet, rain or freezing rain. Winds SE to SSW at 5-10 mph, with higher gusts, on middle-upper elevation mountain ridges and exposed plateaus. Damp and raw with temperatures in the mid-upper 30s.
Saturday Night Into Sunday Morning
Mainly rain. Freezing rain remaining possible in upslope locations at upper elevations in the High Knob Massif. SE to S winds 5-15 mph, with higher gusts, below 2500 to 3000 feet. SSE-S winds 10-20 mph and gusty at upper elevations. Temperatures widespread in the 30s. Areas of fog and low clouds, especially at upper elevations. Wind chills in the 20s to lower 30s, except 10s in gusts on higher peaks.
Sunday Afternoon-Early Evening
Rain or freezing rain changing back to snow at upper elevations first, then within middle-lower elevations by late in this period.
Dropping cloud bases with fog becoming dense at middle to upper elevations along and north of the High Knob Massif-Tennessee Valley Divide. Light winds shifting NW-N at mainly 10 mph or less.
Temperatures dropping into upper 20s to mid 30s.
Sunday Night Into Monday Morning
Light snow and snow showers. Freezing fog at mid-upper elevations along and north of the High Knob Massif-Tennessee Valley Divide. NW winds mostly less than 10 mph. Temperatures dropping into the middle-upper 20s, varying from low 20s at highest elevations in the High Knob Massif to lower 30s in downslope locations toward the south.
*Snowfall Forecast – Saturday To Monday
Up to 1″ at elevations below 2500 feet
Up to 2″ at elevations above 3000 feet
Target Snowfall of 0.5″ to 1″ in Norton-Wise area (+/-) 0.5″ error potential, suggesting a dusting to 1″ possible during entire event. This is a relatively low confidence forecast.
Snowfall totals are for locations along and northwest to northeast of the High Knob Massif-Tennessee Valley Divide, with lesser amounts expected to generally fall toward the south within downslope locations of the Clinch, Powell, and Holston valleys.
*Stay tuned for later adjustments depending upon how the system evolves into Sunday.
Weather Discussion ( Miller B = Nasty )
Saturday Afternoon Update
Following a light coating of snow into Saturday AM across northern parts of Wise, Dickenson & Buchanan counties the day has featured a break and widespread temperatures hovering in the 30s to near 40.
While snow began falling on High Knob between 1-2 AM Saturday, subsequent precipitation evaporated as dewpoints tanked ( going sub-zero ) to suggest that sinking air aloft was being generated and completely missed by forecast models which predicted saturation from top to bottom over time.
Based upon new model runs today I have greatly reduced snow amounts into Monday; however, this continues to be a low confidence forecast setting.
Using past climatology of Miller B systems, rain should dominate from this point forward westward of the cold air damming wedge, with a transition back to snow as winds shift northerly in direction late Sunday into Monday. Since this system will not deepen into a Nor’easter, snow amounts should remain light and limited in backside upslope flow.
A notable exception to the above being a continued threat of icing at upper elevations in the High Knob Massif where air temps-dewpoints remain supportive of freezing rain, which I have left in my forecast for upper elevations.
Outside of freezing rain, there is nothing worse and more nasty than a cold rain during winter with air temperatures in the 30s. NASTY!
Previous January 11 Discussion
The upcoming winter storm is forecast by models to take on characteristics of a Miller B system. My past climatology of such storms can be summarized by a single word. NASTY.
Miller B storms tend to throw everything but the proverbial kitchen sink down on the mountain area, and this event will be no different if it does indeed conform to this type of winter storm.
By nature, Miller B events tend to be among the most difficult to forecast with respect to specific amounts of any given precipitation type.
Some Miller B storm systems become Nor’easters.
Some Miller B storms ( like this one ) take a trajectory which carries them outward into the Atlantic Ocean and do not turn up the coast toward New England.
NAM 12 KM Model Total Snowfall Forecast_Next 60-Hours
A large difference in snowfall amounts between the NAM 12 KM and its high-resolution 3 KM sibling can be used to illustrate the forecast difficulties.
NAM 3 KM Model Total Snowfall Forecast_Next 60-Hours
The 12z run of the operational European Model and many ensembles are closer to the NAM 12 KM locally, but more like the NAM 3 KM toward the south where it transports more above freezing air aloft across the Tennessee Valley and southern Appalachians.
The European Model group and the NAM 3 KM are predicting a setting for significant icing across much of North Carolina versus the GFS-FV3 and NAM 12 KM .
GFS-FV3 Model Total Snowfall Forecast_Next 84-Hours
The new GFS-FV3 looks too heavy over the Carolinas and more on target for the Greenbrier Valley region of southeastern West Virginia where past climo on Miller B storms shows a maximum in snow.
Totals of frozen precipitation types within upper elevations of the High Knob Massif also tend to be greater than generally indicated by models in this type of Miller B storm setting.
Government Shut-Down & USA Models
Is the current government shut-down impacting daily forecasts in the USA?
It should not in theory, but since high-resolution USA models use the GFS domain it is problematic. It is not surprising that the GFS has generally struggled with rather significant inconsistencies and it is scheduled for a replacement upgrade to a new dynamical core being called the FV3 for Finite Volume Cubed-Sphere.
While the GFS-FV3 has been in testing mode, it is not yet the official USA model domain for running of the high-resolution terrain models.
The ECMWF and its ensemble mean has been my favored medium range model since I first began using it during the early 1990’s; however, being global in nature it is not designed for detailed topographic resolution.
No model ever generates a totally perfect forecast, especially in complex terrain settings, and all must be adjusted to best fit local terrain and climatology.
Yet, the better a model performs the better any forecast can theoretically become.
A mostly unspoken factor, but extremely valid, is stress-strain this is putting upon employees of the National Weather Service and their families. This entire aspect is simply wrong.
Members of the NWS are professionals and while they typically carry onward this is not their fault and they should not be penalized for their public service which, unfortunately, they typically do not receive the credit they deserve even without a shut-down.
Cold Blast of January 10-11
Temperatures plunged into the single digits and 10s with this first major cold blast of January 2019, not including wind chills, with a large vertical spread developing this morning ( Friday Jan 11 ) between rising readings into 20s on high mountain ridges versus temps dropping toward 0 degrees in high valleys ( hovering near 10 degrees in Clintwood ).
MAX temperatures January 10 did not rise above lower-mid 10s at highest elevations in the massif, versus mid-upper 20s around Wise and Clintwood.
Light Snow At 9:41 AM On January 10, 2018_UVA-Wise
This was the first cold frontal passage in months, if not longer, to transport limited moisture.
A dusting up to 1″, with most of the area only having a dusting of snow, was observed as the bulk of Great Lake moisture remained northeast of the area.
While I generally expected this, and noted it on my previous forecast page, moisture was a little slower to arrive on Wednesday and slower to leave upslope sides of the mountains on Thursday.
GOES-16 Visible Image At 12:57 PM on January 10, 2018
The local mountains were on the southwest edge of the moisture field into Thursday afternoon, with clouds banking up against the Wise County side of the High Knob Massif ( Scott-Lee Counties cleared ) versus clouds which extended farther southeast as air toward the northeast of the massif was not being lifted as efficiently ( allowing solid clouds to reach southeast to the Brumley-Garden mountain area ) nor sinking leeward as vigorously on NNW-NNE winds.
