NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260216_1800
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)
=== ===== === ==== ==== === === === ====
Mon 02/16 18Z 0.08 2005  84  55  -5 0.00
Mon 02/16 19Z 0.08 2005  84  52  -5 0.00
Mon 02/16 20Z 0.12 2105  85  50  -4 0.00
Mon 02/16 21Z 0.14 2206  86  46  -4 0.00
Mon 02/16 22Z 0.14 2206  85  41  -3 0.00
Mon 02/16 23Z 0.12 2107  86  33  -3 0.00
Tue 02/17 00Z 0.14 2108  87  38  -3 0.00
Tue 02/17 02Z 0.22 2112  91  49  -4 0.00
Tue 02/17 03Z 0.29 2213  93  57  -4 0.00
Tue 02/17 04Z 0.36 2315  94  63  -4 0.00
Tue 02/17 05Z 0.34 2414  94  83  -3 0.00
Tue 02/17 06Z 0.36 2415  95  88  -3 0.00
Tue 02/17 07Z 0.32 2314  94  91  -3 0.01
Tue 02/17 08Z 0.30 2214  95  94  -2 0.01
Tue 02/17 09Z 0.29 2214  96  96  -2 0.01
Tue 02/17 10Z 0.28 2214  95  97  -2 0.01
Tue 02/17 11Z 0.30 2216  96  95  -2 0.01
Tue 02/17 12Z 0.36 2218  97  90  -2 0.01
Tue 02/17 13Z 0.39 2217  97  88  -3 0.02
Tue 02/17 14Z 0.36 2415  98  78  -3 0.03
Tue 02/17 15Z 0.37 2514  98  62  -3 0.02
Tue 02/17 18Z 0.28 2912  98  33  -3 0.02
Tue 02/17 19Z 0.29 2912  98  33  -3 0.01
Tue 02/17 22Z 0.32 2914  95  13  -3 0.01
Tue 02/17 23Z 0.38 2915  91  18  -3 0.01
Wed 02/18 00Z 0.41 2817  83  31  -2 0.00
Wed 02/18 01Z 0.40 2818  75  22  -2 0.00
Wed 02/18 02Z 0.47 2821  72  30  -2 0.00
Wed 02/18 03Z 0.45 2922  65  19  -2 0.00
Wed 02/18 04Z 0.43 2923  58  15  -3 0.00
Wed 02/18 05Z 0.45 2924  57  13  -3 0.00
Wed 02/18 06Z 0.44 2924  53  10  -3 0.01
Wed 02/18 07Z 0.43 3025  55   7  -3 0.01
Wed 02/18 08Z 0.39 3025  56   6  -4 0.01
Wed 02/18 09Z 0.33 3024  57   6  -4 0.00
Wed 02/18 10Z 0.31 3023  54   7  -4 0.00
Wed 02/18 11Z 0.24 3122  47   8  -3 0.00
Wed 02/18 12Z 0.22 3120  43  10  -3 0.00
Wed 02/18 13Z 0.17 3117  39  15  -3 0.00
Wed 02/18 14Z 0.16 3114  39  28  -3 0.00
Wed 02/18 15Z 0.14 3112  39  43  -3 0.00
Wed 02/18 16Z 0.16 3010  41  63  -3 0.00
Wed 02/18 17Z 0.14 3009  42  65  -4 0.00
Wed 02/18 18Z 0.11 2906  51  75  -4 0.00
Wed 02/18 19Z 0.07 3004  62  87  -4 0.00
Wed 02/18 21Z 0.03 0004  77  94  -4 0.00
Wed 02/18 22Z 0.04 0103  78  94  -4 0.00
Wed 02/18 23Z 0.06 0204  79  94  -4 0.00
Thu 02/19 00Z 0.08 0305  76  95  -4 0.00
Thu 02/19 01Z 0.04 0203  78  95  -5 0.00
Thu 02/19 03Z 0.04 3506  74  87  -6 0.01
Thu 02/19 05Z 0.03 3508  56  73  -6 0.01

Run total areal avg QPF for the Central_Greens is: 0.23 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