NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260825_0600
Using the MB925 to MB850 layer.
Assumes greens are orthogonal to 270 degree winds.

925-850 mb Layer Average Wind/RH. Avg QPF over the greens.
Date   Time        Wind RH% 700 850T QPF
Day mm/dd hhZ Frd# DDFF (%) RH% (C) (in)
=== ===== === ==== ==== === === === ====
Tue 08/25 06Z 0.33 2212  89  97   9 0.00
Tue 08/25 07Z 0.37 2412  90  94   8 0.00
Tue 08/25 08Z 0.33 2410  92  89   9 0.00
Tue 08/25 09Z 0.29 2409  93  89   9 0.01
Tue 08/25 10Z 0.31 2310  94  92   9 0.01
Tue 08/25 11Z 0.32 2312  95  94   9 0.01
Tue 08/25 12Z 0.34 2512  96  86   9 0.02
Tue 08/25 13Z 0.31 2610  96  84   9 0.01
Tue 08/25 14Z 0.32 2810  95  77   9 0.01
Tue 08/25 15Z 0.35 2910  96  71   9 0.01
Tue 08/25 16Z 0.38 3011  97  67   8 0.01
Tue 08/25 17Z 0.40 3010  96  67   8 0.00
Tue 08/25 18Z 0.38 3009  96  71   8 0.02
Tue 08/25 19Z 0.36 3010  96  73   9 0.06
Tue 08/25 20Z 0.34 3111  93  62   9 0.03
Tue 08/25 21Z 0.33 3111  92  56   9 0.01
Tue 08/25 22Z 0.32 3111  91  60   9 0.02
Tue 08/25 23Z 0.29 3112  89  54  10 0.00
Wed 08/26 00Z 0.28 3113  88  58  10 0.01
Wed 08/26 01Z 0.30 3114  86  54  10 0.01
Wed 08/26 02Z 0.29 3114  87  57   9 0.01
Wed 08/26 03Z 0.28 3213  87  56   9 0.01
Wed 08/26 04Z 0.26 3213  86  53   9 0.01
Wed 08/26 05Z 0.23 3212  85  49   9 0.01
Wed 08/26 06Z 0.25 3112  87  46   9 0.01
Wed 08/26 07Z 0.24 3112  87  44   9 0.01
Wed 08/26 08Z 0.21 3212  85  40  10 0.01
Wed 08/26 09Z 0.18 3211  85  38  10 0.01
Wed 08/26 10Z 0.17 3210  86  36  10 0.01
Wed 08/26 11Z 0.17 3209  86  31  10 0.01
Wed 08/26 12Z 0.16 3108  87  27  10 0.01
Wed 08/26 13Z 0.11 3206  85  21  10 0.01
Wed 08/26 14Z 0.09 3105  84  18  10 0.00
Wed 08/26 15Z 0.10 2904  84  17  10 0.00
Wed 08/26 16Z 0.10 2903  83  15  10 0.00
Wed 08/26 17Z 0.11 2803  82  12  11 0.00
Wed 08/26 18Z 0.12 2704  81   9  11 0.00
Wed 08/26 19Z 0.09 2602  80   8  11 0.00
Wed 08/26 20Z 0.08 2402  79   7  11 0.00
Wed 08/26 21Z 0.09 2303  79   6  11 0.00
Wed 08/26 22Z 0.06 2103  77   5  11 0.00
Wed 08/26 23Z 0.03 1904  77   3  11 0.00
Thu 08/27 00Z 0.05 1905  77   2  12 0.00
Thu 08/27 01Z 0.05 1907  75   3  12 0.00
Thu 08/27 02Z 0.07 1908  71   8  12 0.00
Thu 08/27 03Z 0.08 1909  69  12  12 0.00
Thu 08/27 04Z 0.11 2010  67  17  12 0.00
Thu 08/27 05Z 0.18 2012  64  21  12 0.00
Thu 08/27 06Z 0.22 2113  63  22  12 0.00
Thu 08/27 07Z 0.29 2115  68  23  12 0.00
Thu 08/27 08Z 0.38 2217  73  19  12 0.00
Thu 08/27 09Z 0.44 2219  77  15  11 0.00
Thu 08/27 10Z 0.47 2120  84  15  11 0.00
Thu 08/27 11Z 0.42 2120  82  16  11 0.00
Thu 08/27 12Z 0.39 2121  83  18  12 0.00
Thu 08/27 13Z 0.35 2120  82  17  12 0.00
Thu 08/27 14Z 0.35 2120  88  15  12 0.00
Thu 08/27 15Z 0.35 2020  93  17  12 0.00
Thu 08/27 16Z 0.28 2019  94  24  12 0.00
Thu 08/27 17Z 0.30 1919  96  34  12 0.00

Run total areal avg QPF for the greens is: 0.37 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