National Weather Service United States Department of Commerce

Mixed Precipitation and Gusty Winds Expected Tonight into Thursday

A winter weather and wind advisory is in effect for portions of the North Country from late this afternoon into Thursday evening. A wintry mix of precipitation will quickly overspread the area late this afternoon into tonight, but change to rain by Thursday morning. Gusty winds develop late tonight and continue at times on Thursday. Isolated power outages and locally slick travel expected. Read More >

Subject: NAM3 EXPERIMENTAL Froude Number for the Northern_Greens

Model run: BTV_GRID_D2D_NAM3_20250402_1800
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)
=== ===== === ==== ==== === === === ====
Wed 04/02 18Z 0.05 1502  37  23  -7 0.00
Wed 04/02 19Z 0.11 1504  34  29  -6 0.00
Wed 04/02 20Z 0.14 1608  34  49  -5 0.00
Wed 04/02 21Z 0.17 1612  34  73  -4 0.00
Wed 04/02 22Z 0.24 1617  32  90  -3 0.00
Wed 04/02 23Z 0.18 1820  43  95  -4 0.00
Thu 04/03 00Z 0.18 1820  76  94  -5 0.00
Thu 04/03 01Z 0.22 1722  93  96  -3 0.04
Thu 04/03 02Z 0.24 1727  94  99  -3 0.04
Thu 04/03 03Z 0.28 1732  93  99  -2 0.03
Thu 04/03 04Z 0.29 1735  94  99  -3 0.03
Thu 04/03 05Z 0.28 1838  94  99  -2 0.06
Thu 04/03 06Z 0.24 1841  95  98  -1 0.07
Thu 04/03 07Z 0.16 1843  95  98   0 0.12
Thu 04/03 08Z 0.11 1946  95  97   2 0.18
Thu 04/03 09Z 0.14 1947  94  96   3 0.34
Thu 04/03 10Z 0.14 1950  95  95   3 0.30
Thu 04/03 11Z 0.05 1950  96  93   6 0.21
Thu 04/03 12Z 0.04 1950  97  97   8 0.14
Thu 04/03 13Z 0.06 2050  97  98   7 0.20
Thu 04/03 14Z 0.17 2148  97  90   9 0.11
Thu 04/03 15Z 0.29 2245  97  84   9 0.03
Thu 04/03 16Z 0.45 2344  97  89   8 0.03
Thu 04/03 17Z 0.59 2439  97  72   8 0.02
Thu 04/03 18Z 0.66 2434  96  58   7 0.02
Thu 04/03 19Z 0.64 2433  97  42   8 0.04
Thu 04/03 20Z 0.85 2534  98  27   7 0.05
Thu 04/03 21Z 0.91 2537  92   3   7 0.02
Thu 04/03 22Z 1.03 2536  79   5   7 0.00
Thu 04/03 23Z 1.60 2538  75   3   6 0.00
Fri 04/04 00Z 2.38 2541  78   2   5 0.00
Fri 04/04 01Z 1.90 2644  86   2   4 0.00
Fri 04/04 02Z 1.60 2641  91   3   3 0.00
Fri 04/04 03Z 1.56 2737  94  14   2 0.01
Fri 04/04 04Z 1.50 2838  93   7   1 0.03
Fri 04/04 05Z 1.68 2837  87   5   0 0.01
Fri 04/04 06Z 1.66 2835  83   7  -1 0.01
Fri 04/04 07Z 1.89 2834  79  11  -2 0.00
Fri 04/04 08Z 1.73 2832  82  13  -3 0.00
Fri 04/04 09Z 1.05 2830  83  13  -3 0.00
Fri 04/04 10Z 0.94 2831  86  14  -3 0.00
Fri 04/04 11Z 0.80 2832  88  17  -3 0.00
Fri 04/04 12Z 0.71 2931  88  17  -2 0.01
Fri 04/04 13Z 0.65 2930  87   6  -2 0.01
Fri 04/04 14Z 0.63 2930  83   3  -2 0.01
Fri 04/04 15Z 0.62 2931  79   1  -1 0.01
Fri 04/04 16Z 0.60 3031  74   1  -1 0.01
Fri 04/04 17Z 0.58 3031  73   1   0 0.00
Fri 04/04 18Z 0.56 3130  72   0   0 0.01
Fri 04/04 19Z 0.53 3130  71   0   0 0.00
Fri 04/04 20Z 0.50 3230  68   1   0 0.00
Fri 04/04 21Z 0.44 3230  65   1   0 0.00
Fri 04/04 22Z 0.40 3328  66   1   0 0.00
Fri 04/04 23Z 0.35 3328  61   1   1 0.00
Sat 04/05 00Z 0.28 3426  58   1   2 0.00
Sat 04/05 01Z 0.24 3425  57   2   2 0.01
Sat 04/05 02Z 0.17 3522  54   6   3 0.01
Sat 04/05 03Z 0.11 3520  49   7   3 0.01
Sat 04/05 04Z 0.06 0017  40   7   4 0.00
Sat 04/05 05Z 0.02 0213  37   8   4 0.00

Run total areal avg QPF for the Northern_Greens is: 2.23 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