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_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)
=== ===== === ==== ==== === === === ====
Tue 09/15 06Z 0.17 0214  84   8   7 0.00
Tue 09/15 07Z 0.17 0311  78   7   7 0.00
Tue 09/15 08Z 0.21 0411  74   6   7 0.00
Tue 09/15 09Z 0.23 0610  74   6   7 0.00
Tue 09/15 10Z 0.17 0807  73   6   7 0.00
Tue 09/15 11Z 0.07 1204  75   6   6 0.00
Tue 09/15 12Z 0.05 1505  72   6   7 0.00
Tue 09/15 13Z 0.02 1607  70   7   8 0.00
Tue 09/15 14Z 0.02 1708  69   7   8 0.00
Tue 09/15 15Z 0.07 1907  71   8   8 0.00
Tue 09/15 16Z 0.07 1908  70   8   9 0.00
Tue 09/15 17Z 0.08 1908  70   9   9 0.00
Tue 09/15 18Z 0.10 1909  70   9   9 0.00
Tue 09/15 19Z 0.09 1810  68  10  10 0.00
Tue 09/15 20Z 0.14 1911  67  12  10 0.00
Tue 09/15 21Z 0.21 2013  63  13  11 0.00
Tue 09/15 22Z 0.21 2014  56  15  13 0.00
Tue 09/15 23Z 0.24 2016  53  34  13 0.00
Wed 09/16 00Z 0.23 2018  48  80  14 0.00
Wed 09/16 01Z 0.23 2020  41  89  15 0.00
Wed 09/16 02Z 0.24 2020  40  86  16 0.00
Wed 09/16 03Z 0.27 2120  45  82  15 0.00
Wed 09/16 04Z 0.37 2222  58  87  13 0.00
Wed 09/16 05Z 0.46 2324  63  87  13 0.00
Wed 09/16 06Z 0.51 2425  62  89  12 0.00
Wed 09/16 07Z 0.53 2424  66  97  12 0.00
Wed 09/16 08Z 0.51 2423  67  93  12 0.01
Wed 09/16 09Z 0.49 2521  76  86  12 0.00
Wed 09/16 10Z 0.48 2621  80  86  12 0.00
Wed 09/16 11Z 0.42 2718  85  89  13 0.00
Wed 09/16 12Z 0.38 2717  92  89  14 0.01
Wed 09/16 13Z 0.38 2717  91  80  14 0.01
Wed 09/16 14Z 0.37 2716  92  64  14 0.00
Wed 09/16 15Z 0.35 2715  92  51  14 0.00
Wed 09/16 16Z 0.35 2714  94  47  14 0.00
Wed 09/16 17Z 0.32 2713  97  44  14 0.00
Wed 09/16 18Z 0.28 2710  98  38  14 0.00
Wed 09/16 19Z 0.26 2809  99  42  13 0.00
Wed 09/16 20Z 0.21 2909  98  31  13 0.00
Wed 09/16 21Z 0.16 3008  98  20  13 0.00
Wed 09/16 22Z 0.17 3009  97  17  13 0.00
Wed 09/16 23Z 0.15 3008  93  11  13 0.00
Thu 09/17 00Z 0.14 3107  93  12  12 0.00
Thu 09/17 01Z 0.12 3107  91  12  12 0.00
Thu 09/17 02Z 0.09 3206  89  11  12 0.00
Thu 09/17 03Z 0.09 3106  90  11  12 0.01
Thu 09/17 04Z 0.05 3204  90  10  12 0.01
Thu 09/17 05Z 0.07 3104  91  10  12 0.01
Thu 09/17 06Z 0.09 2803  90  10  12 0.00
Thu 09/17 07Z 0.10 2703  90  10  12 0.00
Thu 09/17 08Z 0.12 2504  92  10  12 0.00
Thu 09/17 09Z 0.13 2505  92  10  11 0.00
Thu 09/17 10Z 0.13 2405  92  10  11 0.00
Thu 09/17 11Z 0.13 2305  92  12  11 0.01
Thu 09/17 12Z 0.13 2305  92  13  11 0.00
Thu 09/17 13Z 0.14 2306  92  14  11 0.01
Thu 09/17 14Z 0.15 2206  91  19  11 0.01
Thu 09/17 15Z 0.18 2208  87  26  11 0.01
Thu 09/17 16Z 0.21 2309  84  37  12 0.00
Thu 09/17 17Z 0.23 2211  76  32  13 0.01

Run total areal avg QPF for the Central_Greens is: 0.11 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