NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260512_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)
=== ===== === ==== ==== === === === ====
Tue 05/12 00Z 0.25 3311  64  80   0 0.00
Tue 05/12 01Z 0.17 3312  65  77  -1 0.00
Tue 05/12 02Z 0.15 3414  64  71  -1 0.00
Tue 05/12 03Z 0.15 3415  66  69  -1 0.00
Tue 05/12 04Z 0.15 3415  68  70  -2 0.00
Tue 05/12 05Z 0.19 3416  68  63  -2 0.00
Tue 05/12 06Z 0.24 3316  67  59  -2 0.00
Tue 05/12 07Z 0.26 3316  65  58  -2 0.00
Tue 05/12 08Z 0.25 3316  65  51  -2 0.00
Tue 05/12 09Z 0.26 3316  65  56  -3 0.00
Tue 05/12 10Z 0.27 3316  65  57  -3 0.00
Tue 05/12 11Z 0.29 3215  63  49  -3 0.00
Tue 05/12 12Z 0.39 3215  63  37  -3 0.00
Tue 05/12 13Z 2.34 3214  65  33  -3 0.00
Tue 05/12 14Z 4.66 3114  64  36  -3 0.00
Tue 05/12 15Z 5.50 3114  63  40  -3 0.00
Tue 05/12 16Z 5.30 3113  62  40  -2 0.00
Tue 05/12 17Z 5.13 3011  62  40  -2 0.00
Tue 05/12 18Z 5.41 3010  62  39  -1 0.00
Tue 05/12 19Z 5.68 3011  63  41  -1 0.00
Tue 05/12 20Z 6.41 2912  64  45   0 0.00
Tue 05/12 21Z 4.86 2910  64  35   0 0.00
Tue 05/12 22Z 2.19 3008  61  29   0 0.00
Tue 05/12 23Z 0.60 3007  59  25   0 0.00
Wed 05/13 00Z 0.54 2808  58  28   0 0.00
Wed 05/13 01Z 0.49 2607  58  27   0 0.00
Wed 05/13 02Z 0.46 2507  58  27   0 0.00
Wed 05/13 03Z 0.49 2508  58  25   0 0.00
Wed 05/13 04Z 0.50 2408  59  17   0 0.00
Wed 05/13 05Z 0.55 2309  59   9   0 0.00
Wed 05/13 06Z 0.55 2310  59   8   0 0.00
Wed 05/13 07Z 0.60 2213  60  46   1 0.00
Wed 05/13 08Z 0.62 2213  63  85   1 0.00
Wed 05/13 09Z 0.61 2214  68  98   1 0.00
Wed 05/13 10Z 0.47 2113  74  96   1 0.00
Wed 05/13 11Z 0.36 2015  83  97   1 0.00
Wed 05/13 12Z 0.26 1916  86  97   2 0.00
Wed 05/13 13Z 0.24 1918  94  91   3 0.01
Wed 05/13 14Z 0.25 1919  96  97   3 0.03
Wed 05/13 15Z 0.27 2020  97  95   4 0.06
Wed 05/13 16Z 0.22 1919  94  90   4 0.02
Wed 05/13 17Z 0.19 1822  96  91   4 0.04
Wed 05/13 18Z 0.23 1924  94  85   5 0.03
Wed 05/13 19Z 0.35 1924  93  92   5 0.01
Wed 05/13 20Z 0.36 1924  96  94   5 0.01
Wed 05/13 21Z 0.32 1925  91  97   5 0.02
Wed 05/13 22Z 0.35 1927  92  93   6 0.01
Wed 05/13 23Z 0.38 1929  95  91   5 0.01
Thu 05/14 00Z 0.43 1931  95  90   5 0.02
Thu 05/14 01Z 0.46 1932  95  80   5 0.01
Thu 05/14 02Z 0.49 2032  95  82   5 0.01
Thu 05/14 03Z 0.48 2033  94  86   5 0.02
Thu 05/14 04Z 0.46 1932  92  83   5 0.02
Thu 05/14 05Z 0.36 1930  93  89   5 0.02
Thu 05/14 06Z 0.26 1929  95  97   5 0.05
Thu 05/14 07Z 0.24 1830  96  99   5 0.07
Thu 05/14 08Z 0.21 1828  96  97   5 0.06
Thu 05/14 09Z 0.15 1827  98  98   5 0.08
Thu 05/14 10Z 0.09 1725  97  97   5 0.05
Thu 05/14 11Z 0.05 1725  96  98   5 0.06

Run total areal avg QPF for the Central_Greens is: 0.72 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