NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260224_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 02/24 06Z 0.36 3227  87  40 -13 0.00
Tue 02/24 07Z 0.40 3231  90  34 -13 0.00
Tue 02/24 08Z 0.30 3328  92  35 -14 0.00
Tue 02/24 09Z 0.25 3325  91  36 -14 0.00
Tue 02/24 10Z 0.26 3223  91  43 -14 0.00
Tue 02/24 11Z 0.29 3122  92  52 -15 0.00
Tue 02/24 12Z 0.27 3121  92  54 -15 0.00
Tue 02/24 13Z 0.24 3119  93  54 -15 0.00
Tue 02/24 14Z 0.26 3118  92  55 -15 0.00
Tue 02/24 15Z 0.32 3017  91  54 -16 0.00
Tue 02/24 16Z 0.36 3018  90  54 -16 0.00
Tue 02/24 17Z 0.36 3017  87  55 -16 0.00
Tue 02/24 18Z 0.42 3017  85  56 -16 0.00
Tue 02/24 19Z 0.61 3016  84  45 -16 0.00
Tue 02/24 20Z 0.60 3014  83  31 -15 0.00
Tue 02/24 22Z 0.67 2813  84   7 -15 0.00
Tue 02/24 23Z 0.72 2715  85   3 -15 0.00
Wed 02/25 00Z 0.66 2716  85   1 -15 0.00
Wed 02/25 01Z 0.51 2715  82   4 -15 0.00
Wed 02/25 02Z 0.40 2614  78   7 -14 0.00
Wed 02/25 03Z 0.29 2513  65  21 -12 0.00
Wed 02/25 04Z 0.23 2411  49  52 -11 0.00
Wed 02/25 05Z 0.25 2314  44  58 -11 0.00
Wed 02/25 06Z 0.31 2318  36  87 -10 0.00
Wed 02/25 07Z 0.31 2218  35  66 -10 0.00
Wed 02/25 08Z 0.25 2119  52  25  -9 0.00
Wed 02/25 09Z 0.25 1924  62  62  -9 0.00
Wed 02/25 10Z 0.28 1928  75  91  -9 0.00
Wed 02/25 11Z 0.30 1932  91  89  -9 0.00
Wed 02/25 12Z 0.31 1932  92  88  -8 0.01
Wed 02/25 13Z 0.38 2029  92  87  -9 0.05
Wed 02/25 14Z 0.44 2125  94  88  -9 0.06
Wed 02/25 15Z 0.50 2121  95  89  -9 0.04
Wed 02/25 16Z 0.61 2217  96  81  -8 0.03
Wed 02/25 17Z 0.86 2215  95  68  -8 0.01
Wed 02/25 18Z 1.91 2315  93  58  -8 0.00
Wed 02/25 19Z 4.38 2317  91  42  -8 0.00
Wed 02/25 20Z 2.85 2319  93  52  -8 0.00
Wed 02/25 21Z 1.27 2319  94  82  -8 0.00
Wed 02/25 22Z 1.01 2320  95  77  -7 0.00
Wed 02/25 23Z 0.87 2222  96  85  -7 0.00
Thu 02/26 00Z 0.99 2323  94  87  -7 0.01
Thu 02/26 01Z 1.42 2522  95  85  -8 0.03
Thu 02/26 02Z 1.65 2624  96  50  -9 0.03
Thu 02/26 03Z 1.42 2626  86  36 -10 0.01
Thu 02/26 04Z 1.11 2725  81  38 -11 0.01
Thu 02/26 05Z 0.87 2722  81  45 -11 0.00
Thu 02/26 06Z 0.90 2621  89  59 -11 0.00
Thu 02/26 07Z 0.91 2621  93  57 -11 0.00
Thu 02/26 08Z 1.12 2624  95  54 -12 0.00
Thu 02/26 09Z 1.35 2726  86  43 -13 0.01
Thu 02/26 10Z 1.24 2728  74  27 -14 0.01
Thu 02/26 11Z 1.30 2731  71  16 -14 0.00
Thu 02/26 12Z 1.29 2732  66  11 -15 0.00
Thu 02/26 13Z 1.46 2731  66   6 -15 0.00
Thu 02/26 14Z 1.96 2728  70   5 -16 0.00
Thu 02/26 15Z 9.40 2725  75   4 -16 0.00
Thu 02/26 16Z 15.67 2724  80   5 -16 0.00
Thu 02/26 17Z 15.68 2724  79   7 -16 0.00

Run total areal avg QPF for the Central_Greens is: 0.31 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