NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260505_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 05/05 00Z 1.05 2320  55  68   8 0.00
Tue 05/05 01Z 0.99 2321  53  60   8 0.00
Tue 05/05 02Z 0.91 2322  51  45   9 0.00
Tue 05/05 03Z 0.88 2225  51  47   9 0.00
Tue 05/05 04Z 0.95 2130  50  62   8 0.00
Tue 05/05 05Z 1.03 2234  57  77   8 0.00
Tue 05/05 06Z 0.98 2236  63  76   9 0.00
Tue 05/05 07Z 0.93 2235  63  70   9 0.00
Tue 05/05 08Z 0.88 2234  64  25   9 0.00
Tue 05/05 09Z 0.84 2331  66  36   8 0.00
Tue 05/05 10Z 0.81 2329  71  74   8 0.01
Tue 05/05 11Z 0.69 2326  73  81   9 0.00
Tue 05/05 12Z 0.94 2332  87  90   7 0.01
Tue 05/05 13Z 0.79 2430  88  88   8 0.04
Tue 05/05 14Z 0.99 2330  86  87   8 0.01
Tue 05/05 15Z 0.95 2329  80  73   9 0.01
Tue 05/05 16Z 1.50 2326  73  55  10 0.00
Tue 05/05 17Z 7.21 2225  67  60  10 0.00
Tue 05/05 18Z 11.37 2125  64  57  11 0.00
Tue 05/05 19Z 13.16 2128  61  52  12 0.00
Tue 05/05 20Z 9.02 2130  69  69  12 0.02
Tue 05/05 21Z 6.66 2133  70  83  12 0.04
Tue 05/05 22Z 3.05 2130  67  88  12 0.08
Tue 05/05 23Z 1.54 2133  67  85  12 0.00
Wed 05/06 00Z 1.74 2435  85  97   9 0.23
Wed 05/06 01Z 0.96 2530  92  94   9 0.13
Wed 05/06 02Z 0.82 2528  94  96   9 0.09
Wed 05/06 03Z 0.71 2524  94  96   9 0.03
Wed 05/06 04Z 0.74 2523  98  95   7 0.04
Wed 05/06 05Z 0.54 2420  96  93   8 0.04
Wed 05/06 06Z 0.45 2418  97  88   7 0.04
Wed 05/06 07Z 0.36 2315  97  71   8 0.03
Wed 05/06 08Z 0.29 2215  96  63   8 0.01
Wed 05/06 09Z 0.27 2117  96  76   8 0.01
Wed 05/06 10Z 0.25 2018  92  66   9 0.00
Wed 05/06 11Z 0.29 2023  91  76   9 0.01
Wed 05/06 12Z 0.41 2026  94  76   8 0.01
Wed 05/06 13Z 0.51 2127  95  88   8 0.02
Wed 05/06 14Z 0.57 2128  96  82   8 0.06
Wed 05/06 15Z 0.55 2026  96  80   8 0.06
Wed 05/06 16Z 0.52 2024  97  84   8 0.04
Wed 05/06 17Z 0.43 2022  98  93   8 0.05
Wed 05/06 18Z 0.42 2023  98  98   8 0.12
Wed 05/06 19Z 0.43 2025  97  99   7 0.18
Wed 05/06 20Z 0.33 1924  99  98   7 0.07
Wed 05/06 21Z 0.40 2121  99  97   7 0.13
Wed 05/06 22Z 0.28 2117  99  98   7 0.08
Wed 05/06 23Z 0.20 2211  99  98   7 0.07
Thu 05/07 00Z 0.19 2509  99  98   6 0.06
Thu 05/07 01Z 0.18 2910  98  99   5 0.05
Thu 05/07 02Z 0.18 3114  96  99   3 0.04
Thu 05/07 03Z 0.22 3117  92  99   2 0.06
Thu 05/07 04Z 0.24 3119  82  98   1 0.02
Thu 05/07 05Z 0.22 3220  62  95   1 0.00
Thu 05/07 06Z 0.25 3220  59  66   0 0.00
Thu 05/07 07Z 0.31 3119  67  49   0 0.00
Thu 05/07 08Z 0.33 3018  80  20   0 0.00
Thu 05/07 09Z 0.37 3018  88   9   0 0.00
Thu 05/07 10Z 0.39 2918  85   7   0 0.00
Thu 05/07 11Z 0.54 2820  76  10  -1 0.00

Run total areal avg QPF for the Central_Greens is: 2.00 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