NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260423_0000
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)
=== ===== === ==== ==== === === === ====
Thu 04/23 00Z 0.19 2307  89  89   2 0.00
Thu 04/23 01Z 0.24 2509  88  72   2 0.00
Thu 04/23 02Z 0.23 2709  85  49   2 0.00
Thu 04/23 03Z 0.24 2810  84  40   2 0.00
Thu 04/23 04Z 0.24 2911  84  59   2 0.00
Thu 04/23 05Z 0.26 2912  79  66   2 0.00
Thu 04/23 06Z 0.28 2913  73  81   2 0.00
Thu 04/23 07Z 0.34 2915  71  81   2 0.00
Thu 04/23 08Z 0.41 2917  68  77   2 0.00
Thu 04/23 09Z 0.47 3020  72  75   2 0.00
Thu 04/23 10Z 0.41 3122  78  78   1 0.00
Thu 04/23 11Z 0.27 3222  76  58   0 0.00
Thu 04/23 12Z 0.25 3222  75  41   0 0.00
Thu 04/23 13Z 0.32 3223  79  18  -1 0.00
Thu 04/23 14Z 0.54 3324  87   8  -2 0.00
Thu 04/23 15Z 2.63 3224  85   9  -3 0.00
Thu 04/23 16Z 4.14 3223  84   8  -2 0.00
Thu 04/23 17Z 4.62 3221  72   6  -2 0.00
Thu 04/23 18Z 5.02 3221  63   5  -2 0.00
Thu 04/23 19Z 5.02 3220  60   4  -1 0.00
Thu 04/23 20Z 4.53 3220  57   4  -1 0.00
Thu 04/23 21Z 4.26 3221  54   4  -1 0.00
Thu 04/23 22Z 2.77 3322  52   2  -1 0.00
Thu 04/23 23Z 0.91 3323  52   2  -1 0.00
Fri 04/24 00Z 0.56 3325  52   2  -2 0.00
Fri 04/24 02Z 0.42 3326  54   4  -3 0.00
Fri 04/24 03Z 0.29 3423  57   4  -3 0.00
Fri 04/24 05Z 0.11 3516  63   5  -4 0.00
Fri 04/24 06Z 0.10 3414  68   4  -5 0.00
Fri 04/24 07Z 0.07 3413  73   5  -5 0.00
Fri 04/24 08Z 0.08 3414  77   7  -6 0.00
Fri 04/24 09Z 0.12 3315  79   9  -6 0.00
Fri 04/24 13Z 0.03 3417  74  45  -5 0.00
Fri 04/24 16Z 0.60 3413  67  51  -5 0.00
Fri 04/24 19Z 0.84 3414  49  50  -3 0.00
Fri 04/24 20Z 0.53 3412  50  51  -3 0.00
Fri 04/24 21Z 0.32 3412  55  34  -3 0.00
Fri 04/24 22Z 0.49 3511  61  17  -3 0.00
Fri 04/24 23Z 0.56 0011  67  10  -3 0.00
Sat 04/25 00Z 0.41 0111  72   8  -3 0.00
Sat 04/25 01Z 0.61 0312  74   7  -4 0.00
Sat 04/25 02Z 0.70 0415  74   9  -4 0.00
Sat 04/25 03Z 0.58 0515  73  14  -4 0.00
Sat 04/25 04Z 0.44 0514  72  17  -4 0.00
Sat 04/25 05Z 0.32 0510  71  18  -4 0.00
Sat 04/25 06Z 0.23 0508  69  18  -3 0.00
Sat 04/25 07Z 0.16 0606  67  18  -3 0.00
Sat 04/25 08Z 0.13 0605  62  20  -2 0.00
Sat 04/25 09Z 0.13 0705  61  23  -2 0.00
Sat 04/25 10Z 0.11 0704  60  23  -2 0.00
Sat 04/25 11Z 0.12 0904  61  22  -3 0.00

Run total areal avg QPF for the Central_Greens is: 0.00 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