NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260721_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 07/21 06Z 0.55 2019  74  26  12 0.00
Tue 07/21 07Z 0.64 2123  75  18  12 0.00
Tue 07/21 08Z 0.79 2126  79  12  11 0.00
Tue 07/21 09Z 0.74 2125  79  13  11 0.00
Tue 07/21 10Z 0.67 2125  82   9  11 0.00
Tue 07/21 11Z 0.57 2026  82   9  12 0.00
Tue 07/21 12Z 0.55 2028  84  12  12 0.00
Tue 07/21 13Z 0.48 1928  86  17  12 0.00
Tue 07/21 14Z 0.37 1926  90  27  12 0.00
Tue 07/21 15Z 0.28 1826  90  57  13 0.00
Tue 07/21 16Z 0.30 1827  90  59  13 0.00
Tue 07/21 17Z 0.23 1829  91  76  14 0.02
Tue 07/21 18Z 0.20 1731  92  66  14 0.00
Tue 07/21 19Z 0.11 1732  93  54  13 0.00
Tue 07/21 20Z 0.04 1733  95  70  14 0.03
Tue 07/21 21Z 0.06 1734  97  61  15 0.05
Tue 07/21 22Z 0.13 1733  97  51  15 0.04
Tue 07/21 23Z 0.11 1730  97  86  15 0.04
Wed 07/22 00Z 0.31 1928  94  81  15 0.19
Wed 07/22 01Z 0.32 1922  93  78  15 0.06
Wed 07/22 02Z 0.32 2019  91  81  15 0.01
Wed 07/22 03Z 0.30 2019  92  89  15 0.12
Wed 07/22 04Z 0.33 2020  96  83  14 0.12
Wed 07/22 05Z 0.36 2020  94  84  14 0.02
Wed 07/22 06Z 0.55 2224  99  68  15 0.05
Wed 07/22 07Z 0.71 2424  99  56  14 0.05
Wed 07/22 08Z 0.67 2322  96  67  14 0.02
Wed 07/22 09Z 0.71 2423  97  74  14 0.02
Wed 07/22 10Z 0.71 2322  97  72  14 0.02
Wed 07/22 11Z 0.72 2322  96  62  14 0.02
Wed 07/22 12Z 0.75 2423  94  49  14 0.01
Wed 07/22 13Z 0.75 2423  91  43  13 0.01
Wed 07/22 14Z 0.73 2423  87  49  14 0.01
Wed 07/22 15Z 0.81 2423  88  42  13 0.01
Wed 07/22 16Z 0.88 2422  89  33  13 0.01
Wed 07/22 17Z 1.04 2421  89  19  12 0.01
Wed 07/22 18Z 1.78 2421  89   9  12 0.00
Wed 07/22 19Z 7.92 2420  84   6  11 0.00
Wed 07/22 20Z 5.98 2520  82  10  11 0.00
Wed 07/22 21Z 3.24 2520  82  15  10 0.00
Wed 07/22 22Z 2.26 2521  85  24   9 0.00
Wed 07/22 23Z 1.60 2521  87  32   9 0.00
Thu 07/23 00Z 1.40 2623  85  31   8 0.00
Thu 07/23 01Z 1.41 2625  89  27   7 0.00
Thu 07/23 02Z 1.15 2626  91  20   7 0.00
Thu 07/23 03Z 0.97 2724  93  13   7 0.00
Thu 07/23 04Z 0.86 2722  96  16   6 0.00
Thu 07/23 05Z 0.71 2820  95  21   6 0.01
Thu 07/23 06Z 0.62 2820  92  18   6 0.00
Thu 07/23 07Z 0.57 2819  91  19   6 0.00
Thu 07/23 08Z 0.55 2819  91  17   6 0.00
Thu 07/23 09Z 0.48 2920  89  17   6 0.00
Thu 07/23 10Z 0.45 3022  88  13   6 0.00
Thu 07/23 11Z 0.42 3023  89  14   6 0.00
Thu 07/23 12Z 0.36 3123  89  17   6 0.00
Thu 07/23 13Z 0.29 3224  85  22   6 0.00
Thu 07/23 14Z 0.29 3221  76  21   6 0.00
Thu 07/23 15Z 0.51 3219  74  22   6 0.00
Thu 07/23 16Z 1.05 3116  71  23   6 0.00
Thu 07/23 17Z 3.43 3013  76  27   6 0.00

Run total areal avg QPF for the Central_Greens is: 0.95 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