Try this. I've had to change the base layer since this FEMA WMS layer doesn't support the web mercator projection. <map initialextent="-78.6133 36.5172 -70.7801 40.1042" top="40">
<basemaps>
<layer label="Aerial" type="tiled" visible="true"
url="http://server.arcgisonline.com/ArcGIS/rest/services/ESRI_Imagery_World_2D/MapServer"/>
</basemaps>
<operationallayers>
<layer label="FEMA WMS" type="wms" visible="true"
url="http://hazards.fema.gov/wmsconnector/wmsconnector/com.esri.wms.Esrimap/NFHL"
version="1.1.1"
skipgetcapabilities="true"
visiblelayers="HDM:DFIRM_COMMUNITY_AVAILABILITY,Flood_Hazard_Zones_General,Flood_Hazard_Zones_linear,USGS_Quads,REF:HYDRO_UNIT_CODE,PLSS_Township_Range_Lines,Base_Flood_Elevation,Flood Hazards Zone Boundaries,Bench_Marks"/>
</operationallayers>
</map>
You can also use the web map directly like this:<map itemid="43f091535c3d413a97bcf28b94594f43" top="40"/>
If your browser window is too big, the service will not appear and will instead return this error message: [ERR0924] Requested image is too big and cannot be created.