NAM3 EXPERIMENTAL Froude Number for the Northern Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Northern_Greens

Model run: BTV_GRID_D2D_NAM3_20260212_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)
=== ===== === ==== ==== === === === ====
Thu 02/12 06Z 0.80 3320  93  73 -14 0.00
Thu 02/12 07Z 0.72 3322  95  69 -14 0.00
Thu 02/12 08Z 0.64 3323  95  67 -13 0.01
Thu 02/12 09Z 0.56 3322  95  65 -13 0.01
Thu 02/12 10Z 0.47 3321  94  64 -13 0.01
Thu 02/12 11Z 0.40 3421  93  62 -13 0.01
Thu 02/12 12Z 0.38 3421  94  63 -13 0.00
Thu 02/12 13Z 0.36 3421  94  68 -13 0.00
Thu 02/12 16Z 0.41 3319  93  59 -13 0.00
Thu 02/12 17Z 0.47 3220  93  51 -13 0.00
Thu 02/12 18Z 0.50 3220  93  29 -13 0.00
Thu 02/12 19Z 0.52 3221  92  10 -13 0.00
Thu 02/12 20Z 0.55 3221  89   6 -13 0.00
Thu 02/12 21Z 0.50 3222  76  10 -12 0.00
Thu 02/12 22Z 0.38 3323  66  12 -11 0.00
Thu 02/12 23Z 0.31 3424  66  13 -10 0.00
Fri 02/13 00Z 0.29 3424  71  14 -10 0.00
Fri 02/13 01Z 0.30 3424  72  14 -10 0.01
Fri 02/13 02Z 0.27 3423  71  14 -10 0.01
Fri 02/13 03Z 0.24 3421  69  14 -10 0.00
Fri 02/13 04Z 0.22 3419  67  15  -9 0.00
Fri 02/13 05Z 0.21 3418  64  17  -9 0.00
Fri 02/13 06Z 0.22 3318  61  20  -9 0.00
Fri 02/13 07Z 0.23 3317  60  22  -9 0.00
Fri 02/13 08Z 0.24 3217  61  28  -9 0.00
Fri 02/13 09Z 0.27 3218  64  32 -10 0.00
Fri 02/13 10Z 0.30 3118  65  30 -10 0.00
Fri 02/13 11Z 0.32 3119  66  30 -10 0.00
Fri 02/13 12Z 0.35 3120  69  18 -10 0.00
Fri 02/13 13Z 0.36 3021  72  14 -10 0.00
Fri 02/13 14Z 0.33 3019  73  16 -10 0.00
Fri 02/13 15Z 0.31 3017  75  19 -10 0.00
Fri 02/13 16Z 0.32 2917  77  19 -11 0.00
Fri 02/13 17Z 0.34 2917  77  17 -11 0.00
Fri 02/13 18Z 0.36 2917  75  18 -11 0.00
Fri 02/13 19Z 0.38 2816  73  35 -11 0.00
Fri 02/13 20Z 0.40 2816  71  63 -11 0.00
Fri 02/13 21Z 0.44 2717  68  52 -11 0.00
Fri 02/13 22Z 0.49 2719  66  44 -11 0.00
Fri 02/13 23Z 0.52 2719  62  50 -11 0.00
Sat 02/14 00Z 0.46 2619  55  55 -10 0.00
Sat 02/14 01Z 0.41 2618  49  52  -9 0.00
Sat 02/14 02Z 0.39 2618  49  62  -9 0.00
Sat 02/14 03Z 0.43 2618  58  65  -9 0.00
Sat 02/14 04Z 0.42 2618  59  67  -9 0.00
Sat 02/14 05Z 0.37 2617  83  81  -9 0.00
Sat 02/14 06Z 0.36 2616  93  80 -10 0.00
Sat 02/14 07Z 0.38 2615  95  86 -10 0.00
Sat 02/14 08Z 0.40 2714  96  89 -11 0.01
Sat 02/14 09Z 0.40 2814  96  86 -11 0.01
Sat 02/14 10Z 0.42 2815  96  86 -11 0.01
Sat 02/14 11Z 0.43 2815  96  86 -10 0.01
Sat 02/14 12Z 0.46 2816  96  88 -10 0.01
Sat 02/14 13Z 0.51 2918  95  85 -10 0.01
Sat 02/14 14Z 0.59 2920  96  84 -11 0.01
Sat 02/14 15Z 0.60 3020  97  34 -11 0.01
Sat 02/14 16Z 0.64 3019  97  16 -11 0.01
Sat 02/14 17Z 0.67 2919  90  27 -12 0.01

Run total areal avg QPF for the Northern_Greens is: 0.16 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