NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260819_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 08/19 06Z 0.07 3002  85  10  12 0.00
Wed 08/19 07Z 0.11 2803  83  11  12 0.00
Wed 08/19 08Z 0.18 2804  83  12  12 0.00
Wed 08/19 09Z 0.19 2604  83  13  12 0.00
Wed 08/19 10Z 0.16 2504  83  17  12 0.00
Wed 08/19 11Z 0.18 2405  84  24  12 0.00
Wed 08/19 12Z 0.18 2206  86  38  12 0.00
Wed 08/19 13Z 0.22 2208  86  47  12 0.00
Wed 08/19 14Z 0.26 2208  86  56  12 0.00
Wed 08/19 15Z 0.32 2209  81  57  12 0.00
Wed 08/19 16Z 0.50 2310  76  60  12 0.00
Wed 08/19 17Z 1.45 2311  77  70  12 0.00
Wed 08/19 18Z 1.71 2311  73  73  13 0.00
Wed 08/19 19Z 1.34 2312  75  70  13 0.00
Wed 08/19 20Z 1.38 2313  80  78  13 0.00
Wed 08/19 21Z 0.86 2313  82  94  13 0.00
Wed 08/19 22Z 0.72 2314  85  90  13 0.00
Wed 08/19 23Z 0.88 2318  92  88  13 0.00
Thu 08/20 00Z 0.76 2420  95  73  13 0.03
Thu 08/20 01Z 0.79 2620  93  50  13 0.02
Thu 08/20 02Z 0.76 2720  96  34  13 0.02
Thu 08/20 03Z 0.56 2919  91  21  13 0.03
Thu 08/20 04Z 0.43 3018  80  10  12 0.01
Thu 08/20 05Z 0.44 3018  71  10  12 0.01
Thu 08/20 06Z 0.39 3017  75   8  11 0.00
Thu 08/20 07Z 0.42 3017  78   6  11 0.00
Thu 08/20 08Z 0.36 3117  74  11  10 0.00
Thu 08/20 09Z 0.29 3115  72   6  10 0.00
Thu 08/20 10Z 0.30 3114  71   8  10 0.00
Thu 08/20 11Z 0.24 3112  70   4  10 0.00
Thu 08/20 12Z 0.26 3111  70   6   9 0.00
Thu 08/20 13Z 0.22 3110  72   8   9 0.00
Thu 08/20 14Z 0.22 3109  75   8   9 0.00
Thu 08/20 15Z 0.22 3106  78   6   9 0.00
Thu 08/20 16Z 0.66 3005  80   9   9 0.00
Thu 08/20 17Z 0.94 2905  78  12   9 0.00
Thu 08/20 18Z 0.68 2805  74   9  10 0.00
Thu 08/20 19Z 0.47 2806  75  10  10 0.00
Thu 08/20 20Z 0.49 2708  81  11  10 0.00
Thu 08/20 21Z 0.39 2608  81  12  10 0.00
Thu 08/20 22Z 0.39 2708  83  11  10 0.00
Thu 08/20 23Z 0.41 2709  87  12   9 0.00
Fri 08/21 00Z 0.37 2908  85  14   9 0.00
Fri 08/21 01Z 0.27 3108  88  12   9 0.00
Fri 08/21 02Z 0.16 3208  89  15   9 0.00
Fri 08/21 03Z 0.04 3408  88  16   8 0.00
Fri 08/21 04Z 0.06 3507  86  17   8 0.00
Fri 08/21 05Z 0.05 3505  84  19   8 0.00
Fri 08/21 06Z 0.04 3506  81  18   9 0.00
Fri 08/21 07Z 0.07 0006  79  18   8 0.00
Fri 08/21 08Z 0.07 0005  79  19   8 0.00
Fri 08/21 09Z 0.14 0305  77  18   8 0.00
Fri 08/21 10Z 0.12 0404  76  20   8 0.00
Fri 08/21 11Z 0.12 0503  75  19   8 0.00
Fri 08/21 12Z 0.11 0603  74  19   8 0.00
Fri 08/21 13Z 0.13 0803  75  15   8 0.00
Fri 08/21 14Z 0.16 1003  78  13   8 0.00
Fri 08/21 15Z 0.33 1204  83  11   8 0.00
Fri 08/21 16Z 0.33 1402  86  10   8 0.00
Fri 08/21 17Z 0.45 1202  87   8   9 0.00

Run total areal avg QPF for the Central_Greens is: 0.12 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