National Weather Service United States Department of Commerce

Light freezing rain and freezing drizzle expected across portions of north central and northeastern Vermont tonight

Areas of light freezing rain and patchy freezing drizzle are expected tonight across portions of north central and northeastern Vermont. Up to a tenth of an inch of ice accumulation is possible which may lead to slick travel. Precipitation will change to areas of light rain or rain showers after 700 am Saturday as temperatures climb above freezing. Read More >

Subject: NAM3 EXPERIMENTAL Froude Number for the Northern_Greens

Model run: BTV_GRID_D2D_NAM3_20260307_0600
Using the MB925 to MB850 layer.
Assumes Northern_Greens are orthogonal to 290 degree winds.

925-850 mb Layer Average Wind/RH. Avg QPF over the Northern_Greens.
Date   Time        Wind RH% 700 850T QPF
Day mm/dd hhZ Frd# DDFF (%) RH% (C) (in)
=== ===== === ==== ==== === === === ====
Sat 03/07 06Z 0.08 2028  91  34   4 0.00
Sat 03/07 07Z 0.08 2031  88  40   5 0.00
Sat 03/07 08Z 0.10 2134  76  50   6 0.00
Sat 03/07 09Z 0.12 2135  75  95   8 0.00
Sat 03/07 10Z 0.13 2137  77  98   9 0.01
Sat 03/07 11Z 0.14 2139  80  87  10 0.01
Sat 03/07 12Z 0.18 2140  89  90  10 0.01
Sat 03/07 14Z 0.34 2341  97  97   9 0.08
Sat 03/07 15Z 0.38 2336  98  96   9 0.17
Sat 03/07 16Z 0.42 2433  97  91   9 0.11
Sat 03/07 17Z 0.45 2435  97  80  10 0.05
Sat 03/07 18Z 0.45 2436  93  91  11 0.01
Sat 03/07 19Z 0.44 2337  88  92  11 0.01
Sat 03/07 20Z 0.44 2340  92  83  11 0.01
Sat 03/07 21Z 0.43 2340  91  78  11 0.00
Sat 03/07 22Z 0.47 2342  89  25  11 0.00
Sat 03/07 23Z 0.55 2444  84  81  11 0.00
Sun 03/08 00Z 0.50 2342  78  86  12 0.00
Sun 03/08 01Z 0.58 2346  89  91  11 0.00
Sun 03/08 02Z 0.64 2446  96  94  10 0.01
Sun 03/08 03Z 0.78 2445  95  54   9 0.06
Sun 03/08 04Z 0.80 2542  95  49   9 0.05
Sun 03/08 05Z 0.69 2537  96  80   9 0.01
Sun 03/08 06Z 0.67 2536  96  80   9 0.02
Sun 03/08 07Z 0.62 2532  91  74   9 0.03
Sun 03/08 08Z 0.63 2533  90  73   9 0.02
Sun 03/08 09Z 0.70 2437  94  77   8 0.03
Sun 03/08 10Z 0.81 2436  96  11   6 0.03
Sun 03/08 11Z 1.14 2439  92  10   4 0.01
Sun 03/08 12Z 1.37 2539  94  11   2 0.01
Sun 03/08 13Z 1.23 2639  94   5   0 0.01
Sun 03/08 14Z 1.12 2637  94   3   0 0.02
Sun 03/08 15Z 1.11 2734  94   3  -1 0.01
Sun 03/08 16Z 1.10 2733  96   5  -2 0.01
Sun 03/08 17Z 1.14 2731  97   5  -3 0.01
Sun 03/08 18Z 0.98 2728  96   5  -3 0.01
Sun 03/08 19Z 0.72 2723  96   5  -3 0.01
Sun 03/08 20Z 0.63 2623  94   8  -2 0.00
Sun 03/08 21Z 0.70 2626  94  12  -2 0.00
Sun 03/08 22Z 0.68 2529  80  21  -1 0.00
Sun 03/08 23Z 0.63 2532  62  87   0 0.00
Mon 03/09 00Z 0.63 2535  60  83   0 0.00
Mon 03/09 01Z 0.94 2541  72  34  -2 0.00
Mon 03/09 02Z 1.18 2641  88  12  -3 0.00
Mon 03/09 03Z 1.14 2739  91  10  -3 0.00
Mon 03/09 04Z 1.03 2737  84  19  -2 0.00
Mon 03/09 05Z 0.84 2734  73  30  -1 0.00
Mon 03/09 06Z 0.81 2732  69  37   0 0.00
Mon 03/09 07Z 0.80 2731  66  44   0 0.00
Mon 03/09 08Z 0.74 2729  60  52   0 0.00
Mon 03/09 09Z 0.66 2629  58  61   1 0.00
Mon 03/09 10Z 0.56 2529  62  70   2 0.00
Mon 03/09 11Z 0.63 2532  72  84   2 0.00
Mon 03/09 12Z 0.58 2532  71  84   2 0.00
Mon 03/09 13Z 0.51 2433  67  78   4 0.00
Mon 03/09 14Z 0.46 2336  52  58   5 0.00
Mon 03/09 15Z 0.45 2340  48  32   6 0.00
Mon 03/09 16Z 0.50 2342  45  42   6 0.00
Mon 03/09 17Z 0.57 2341  45  51   7 0.00

Run total areal avg QPF for the Northern_Greens is: 0.83 inches.

Froude Number (Frd#): 
Frd# < 0.5 Flow is subcritical and blocked.
         Upslope clouds/precip backed farther upwind of and up to mtn crest.
         W Upslope snow favors eastern Champlain Valley, BTV, and Western slopes.
         Gap winds possible.
Frd# 0.5-1 Flow is subcritical/slow moving/blocked.
         Upslope clouds/precip falls immediately upwind of mtn crest.
         W Upslope snow favors western slopes to the Green Mt. spine including:
         Montgomery,Underhill,Jericho,Bolton,Richmond,Huntington,Lincoln.
         Gap winds possible.
Frd# 1-2 Flow is critical.
         With strong winds, Mountain waves/downslope winds possible.
         Precip falls close to mountain ridge crests and on lee side.
         W Upslope snow favors Green Mt Spine,Jay,Stowe,Waterbury,NE Kingdom.
Froude > 2 Flow is supercritical/unblocked(rapid flow).
         Air flows freely over terrain.
         Persistent upslope snow not favored. Scattered snow showers and flurries.

Relative Humidity (RH): 
         925-850 mb RH > 90% needed for upslope precipitation.
         with 700mb RH > 70% favors upslope snow.
         with 700mb RH > 90% greater amounts of W upslope snow possible.

850mb Temperature (T degC) Westerly Upslope Snow Ratios: (Avg=28:1)
        T > -11       10-15:1
        T -11 to -15  25-35:1
        T < -15       15-20:1