NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260225_0600
Using the MB925 to MB850 layer.
Assumes Central_Greens are orthogonal to 260 degree winds.

925-850 mb Layer Average Wind/RH. Avg QPF over the Central_Greens.
Date   Time        Wind RH% 700 850T QPF
Day mm/dd hhZ Frd# DDFF (%) RH% (C) (in)
=== ===== === ==== ==== === === === ====
Wed 02/25 06Z 0.25 2115  61  41 -12 0.00
Wed 02/25 07Z 0.28 2118  42  59 -11 0.00
Wed 02/25 08Z 0.27 2119  32  40 -10 0.00
Wed 02/25 09Z 0.25 2020  36  56 -10 0.00
Wed 02/25 10Z 0.26 2022  47  90 -10 0.00
Wed 02/25 11Z 0.31 2027  63  95 -10 0.00
Wed 02/25 12Z 0.33 2032  91  88 -10 0.02
Wed 02/25 13Z 0.34 1933  92  86  -9 0.04
Wed 02/25 14Z 0.37 2032  94  87  -9 0.03
Wed 02/25 15Z 0.45 2126  96  75  -8 0.01
Wed 02/25 18Z 0.39 2114  97  87  -7 0.01
Wed 02/25 19Z 0.44 2114  96  89  -7 0.01
Wed 02/25 20Z 0.59 2115  95  46  -7 0.01
Wed 02/25 21Z 0.80 2116  95  70  -7 0.01
Wed 02/25 23Z 0.71 2219  96  78  -6 0.01
Thu 02/26 00Z 0.60 2118  95  79  -6 0.00
Thu 02/26 01Z 0.63 2123  96  87  -5 0.00
Thu 02/26 02Z 0.75 2127  97  90  -5 0.01
Thu 02/26 03Z 0.95 2230  98  92  -5 0.00
Thu 02/26 04Z 1.40 2426  93  84  -6 0.00
Thu 02/26 05Z 1.18 2524  90  79  -7 0.02
Thu 02/26 06Z 1.32 2623  93  78  -8 0.03
Thu 02/26 07Z 1.27 2624  94  30  -9 0.02
Thu 02/26 09Z 2.03 2727  86  35 -12 0.00
Thu 02/26 10Z 1.69 2729  70  35 -13 0.02
Thu 02/26 11Z 1.27 2731  66  29 -13 0.01
Thu 02/26 12Z 1.21 2732  68  13 -14 0.01
Thu 02/26 13Z 1.25 2830  69   4 -14 0.01
Thu 02/26 14Z 1.59 2827  68   2 -15 0.00
Thu 02/26 15Z 5.61 2824  72   4 -15 0.00
Thu 02/26 16Z 6.74 2819  74   6 -15 0.00
Thu 02/26 17Z 9.11 2617  77   8 -15 0.00
Thu 02/26 18Z 7.86 2617  76  10 -14 0.00
Thu 02/26 19Z 8.12 2617  77  11 -14 0.00
Thu 02/26 20Z 8.74 2617  79  13 -13 0.00
Thu 02/26 21Z 6.36 2617  80  18 -13 0.00
Thu 02/26 22Z 3.00 2719  79  30 -13 0.00
Thu 02/26 23Z 1.78 2720  79  34 -13 0.00
Fri 02/27 00Z 1.53 2721  80  41 -14 0.00
Fri 02/27 01Z 1.09 2821  78  52 -14 0.00
Fri 02/27 02Z 0.74 2922  73  48 -14 0.00
Fri 02/27 03Z 0.60 2921  73  44 -14 0.00
Fri 02/27 04Z 0.47 2919  71  41 -13 0.00
Fri 02/27 05Z 0.40 2918  68  38 -13 0.00
Fri 02/27 06Z 0.37 2918  65  41 -12 0.00
Fri 02/27 07Z 0.33 2918  62  41 -11 0.00
Fri 02/27 08Z 0.30 2917  58  46 -10 0.00
Fri 02/27 09Z 0.29 2816  57  49 -10 0.00
Fri 02/27 10Z 0.29 2816  53  65  -9 0.00
Fri 02/27 11Z 0.33 2717  54  70  -9 0.00
Fri 02/27 12Z 0.33 2618  53  73  -8 0.00
Fri 02/27 13Z 0.37 2520  52  77  -7 0.00
Fri 02/27 14Z 0.40 2522  58  84  -6 0.00
Fri 02/27 15Z 0.44 2522  63  88  -6 0.00
Fri 02/27 16Z 0.49 2522  62  83  -5 0.00
Fri 02/27 17Z 0.54 2423  61  74  -5 0.00

Run total areal avg QPF for the Central_Greens is: 0.28 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