NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260915_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)
=== ===== === ==== ==== === === === ====
Tue 09/15 18Z 0.10 1905  77  11   9 0.00
Tue 09/15 19Z 0.11 1906  76  11   9 0.00
Tue 09/15 20Z 0.13 1908  77  11   9 0.00
Tue 09/15 21Z 0.13 1811  75  10   9 0.00
Tue 09/15 22Z 0.15 1913  66  17  11 0.00
Tue 09/15 23Z 0.21 2015  59  41  12 0.00
Wed 09/16 00Z 0.21 2016  51  84  13 0.00
Wed 09/16 01Z 0.25 2018  49  86  13 0.00
Wed 09/16 02Z 0.27 2118  48  83  14 0.00
Wed 09/16 03Z 0.30 2119  48  78  14 0.00
Wed 09/16 04Z 0.31 2219  50  85  14 0.00
Wed 09/16 05Z 0.37 2320  57  94  14 0.00
Wed 09/16 06Z 0.44 2421  60  95  13 0.00
Wed 09/16 07Z 0.51 2423  57  94  13 0.00
Wed 09/16 08Z 0.55 2424  69  95  12 0.00
Wed 09/16 09Z 0.53 2522  70  94  12 0.00
Wed 09/16 10Z 0.46 2619  83  88  13 0.00
Wed 09/16 11Z 0.39 2718  90  83  13 0.02
Wed 09/16 12Z 0.38 2818  95  67  13 0.02
Wed 09/16 13Z 0.37 2818  96  55  14 0.01
Wed 09/16 14Z 0.36 2816  95  47  14 0.01
Wed 09/16 15Z 0.34 2814  93  40  14 0.00
Wed 09/16 16Z 0.33 2813  92  38  14 0.00
Wed 09/16 17Z 0.36 2812  94  32  14 0.00
Wed 09/16 18Z 0.34 2810  96  23  13 0.00
Wed 09/16 19Z 0.33 2811  97  17  13 0.00
Wed 09/16 20Z 0.29 2810  96  16  13 0.00
Wed 09/16 21Z 0.25 2808  95  19  14 0.00
Wed 09/16 22Z 0.21 2907  92  24  14 0.00
Wed 09/16 23Z 0.19 2908  91  22  13 0.00
Thu 09/17 00Z 0.16 2907  89  16  13 0.00
Thu 09/17 01Z 0.17 3007  90  11  13 0.00
Thu 09/17 02Z 0.14 3006  91  10  13 0.01
Thu 09/17 03Z 0.11 3005  91   9  12 0.01
Thu 09/17 04Z 0.08 3205  92   9  12 0.00
Thu 09/17 05Z 0.05 3204  91   9  12 0.00
Thu 09/17 06Z 0.06 3104  91  10  12 0.00
Thu 09/17 07Z 0.08 2903  90  13  12 0.00
Thu 09/17 08Z 0.07 2802  87  21  12 0.00
Thu 09/17 09Z 0.07 2602  86  24  12 0.00
Thu 09/17 10Z 0.07 2303  85  33  13 0.00
Thu 09/17 11Z 0.07 2004  85  38  13 0.00
Thu 09/17 12Z 0.08 1907  85  41  12 0.00
Thu 09/17 13Z 0.12 2008  85  41  12 0.00
Thu 09/17 14Z 0.16 2109  85  45  12 0.00
Thu 09/17 15Z 0.17 2109  85  41  12 0.00
Thu 09/17 16Z 0.20 2110  84  46  13 0.00
Thu 09/17 17Z 0.23 2211  84  50  13 0.00
Thu 09/17 18Z 0.25 2211  81  49  13 0.00
Thu 09/17 19Z 0.29 2312  81  71  13 0.00
Thu 09/17 20Z 0.27 2311  78  83  14 0.00
Thu 09/17 21Z 0.29 2211  83  94  13 0.01
Thu 09/17 22Z 0.28 2211  84  96  13 0.01
Thu 09/17 23Z 0.29 2211  87  97  13 0.01
Fri 09/18 00Z 0.27 2309  90  97  12 0.11
Fri 09/18 01Z 0.25 2308  91  99  13 0.11
Fri 09/18 02Z 0.24 2508  93  93  13 0.06
Fri 09/18 03Z 0.20 2607  95  97  13 0.06
Fri 09/18 04Z 0.21 2707  93  93  13 0.03
Fri 09/18 05Z 0.24 2810  90  90  13 0.02

Run total areal avg QPF for the Central_Greens is: 0.50 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