NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260407_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 04/07 00Z 1.25 2917  76  60  -8 0.00
Tue 04/07 01Z 1.58 2918  73  59  -8 0.00
Tue 04/07 02Z 1.34 2917  73  60  -8 0.00
Tue 04/07 03Z 1.03 2914  74  57  -8 0.00
Tue 04/07 04Z 0.80 2812  74  55  -8 0.00
Tue 04/07 05Z 0.64 2809  73  54  -8 0.00
Tue 04/07 06Z 0.56 2609  73  55  -8 0.00
Tue 04/07 07Z 0.53 2409  71  70  -8 0.00
Tue 04/07 08Z 0.46 2310  67  81  -7 0.00
Tue 04/07 09Z 0.46 2209  68  88  -7 0.00
Tue 04/07 10Z 0.35 2109  78  89  -7 0.00
Tue 04/07 11Z 0.22 2011  88  90  -7 0.00
Tue 04/07 12Z 0.21 1912  94  89  -7 0.01
Tue 04/07 13Z 0.21 2012  97  87  -6 0.02
Tue 04/07 14Z 0.22 2011  98  88  -6 0.02
Tue 04/07 15Z 0.28 2109  98  89  -6 0.02
Tue 04/07 16Z 0.32 2308  98  88  -6 0.03
Tue 04/07 17Z 0.42 2610  97  86  -6 0.04
Tue 04/07 18Z 0.36 2812  95  85  -7 0.02
Tue 04/07 19Z 0.26 3119  94  61  -8 0.02
Tue 04/07 20Z 0.21 3325  92  66  -9 0.01
Tue 04/07 21Z 0.30 3329  84  75 -10 0.01
Tue 04/07 22Z 0.47 3227  81  62 -11 0.00
Tue 04/07 23Z 0.69 3227  85  29 -12 0.00
Wed 04/08 00Z 0.87 3127  84  15 -13 0.00
Wed 04/08 01Z 1.40 3227  70  20 -13 0.00
Wed 04/08 02Z 0.78 3227  55  23 -13 0.00
Wed 04/08 03Z 0.59 3227  50  22 -13 0.00
Wed 04/08 04Z 0.44 3225  47  21 -13 0.00
Wed 04/08 05Z 0.34 3223  44  20 -13 0.00
Wed 04/08 06Z 0.27 3221  45  21 -13 0.00
Wed 04/08 07Z 0.25 3220  45  19 -12 0.00
Wed 04/08 08Z 0.26 3220  45  18 -12 0.00
Wed 04/08 09Z 0.24 3219  45  17 -12 0.00
Wed 04/08 10Z 0.22 3117  43  17 -11 0.00
Wed 04/08 11Z 0.22 3116  41  16 -10 0.00
Wed 04/08 12Z 0.20 3114  38  14 -10 0.00
Wed 04/08 13Z 0.19 3013  36  11  -9 0.00
Wed 04/08 14Z 0.18 3010  33   8  -8 0.00
Wed 04/08 15Z 0.18 2908  31   6  -7 0.00
Wed 04/08 16Z 0.19 2908  27   4  -7 0.00
Wed 04/08 17Z 0.20 2806  24   3  -6 0.00
Wed 04/08 18Z 0.25 2606  22   3  -5 0.00
Wed 04/08 19Z 0.33 2405  21   4  -5 0.00
Wed 04/08 20Z 0.43 2306  21   6  -4 0.00
Wed 04/08 21Z 0.36 2207  21   8  -4 0.00
Wed 04/08 22Z 0.32 2110  21  11  -3 0.00
Wed 04/08 23Z 0.38 2213  21  12  -3 0.00
Thu 04/09 00Z 0.43 2216  19  12  -2 0.00
Thu 04/09 01Z 0.43 2218  19  12  -1 0.00
Thu 04/09 02Z 0.41 2220  22  10   0 0.00
Thu 04/09 03Z 0.40 2222  23  10   0 0.00
Thu 04/09 04Z 0.40 2223  27  10   1 0.00
Thu 04/09 05Z 0.40 2224  22   8   2 0.00
Thu 04/09 06Z 0.40 2225  17   8   2 0.00
Thu 04/09 07Z 0.42 2226  15   8   2 0.00
Thu 04/09 08Z 0.45 2227  12   8   2 0.00
Thu 04/09 09Z 0.48 2229  10   9   2 0.00
Thu 04/09 10Z 0.50 2231   9  11   2 0.00
Thu 04/09 11Z 0.52 2233   8  17   3 0.00

Run total areal avg QPF for the Central_Greens is: 0.20 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